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 $204.46   12.541%   $230.1013   $230.10   $230.10   $230.10  
  Purchase #2 $224.58   10.273%   $247.6511   $247.65   $247.65   $247.70  
  Purchase #3 $80.34   8.179%   $86.911   $86.91   $86.90   $86.90  
  Purchase #4 $218.69   6.466%   $232.8305   $232.83   $232.85   $232.80  
  Purchase #5 $72.91   4.107%   $75.9044   $75.90   $75.90   $75.90  
  Purchase #6 $60.25   11.703%   $67.3011   $67.30   $67.30   $67.30  
  Purchase #7 $157.85   5.380%   $166.3423   $166.34   $166.35   $166.30  
  7 purchase totals = $1,019.08       $1,107.0417   $1,107.03   $1,107.05   $1,107.00