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 $227.55   5.869%   $240.9049   $240.90   $240.90   $240.90  
  Purchase #2 $95.52   11.343%   $106.3548   $106.35   $106.35   $106.40  
  Purchase #3 $239.25   6.161%   $253.9902   $253.99   $254.00   $254.00  
  Purchase #4 $49.30   5.337%   $51.9311   $51.93   $51.95   $51.90  
  Purchase #5 $240.58   8.723%   $261.5658   $261.57   $261.55   $261.60  
  Purchase #6 $151.48   9.451%   $165.7964   $165.80   $165.80   $165.80  
  Purchase #7 $110.42   12.868%   $124.6288   $124.63   $124.65   $124.60  
  7 purchase totals = $1,114.10       $1,205.1720   $1,205.17   $1,205.20   $1,205.20