Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $120.67   3.261%   $124.605   $124.61   $124.60   $124.60  
  Purchase #2 $101.48   5.319%   $106.8777   $106.88   $106.90   $106.90  
  Purchase #3 $191.92   10.466%   $212.0063   $212.01   $212.00   $212.00  
  Purchase #4 $192.46   9.621%   $210.9766   $210.98   $211.00   $211.00  
  Purchase #5 $190.55   10.418%   $210.4015   $210.40   $210.40   $210.40  
  Purchase #6 $155.93   6.393%   $165.8986   $165.90   $165.90   $165.90  
  Purchase #7 $126.45   11.265%   $140.6946   $140.69   $140.70   $140.70  
  7 purchase totals = $1,079.46       $1,171.4603   $1,171.47   $1,171.50   $1,171.50