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 $24.25   11.104%   $26.9427   $26.94   $26.95   $26.90  
  Purchase #2 $170.98   13.477%   $194.023   $194.02   $194.00   $194.00  
  Purchase #3 $229.77   9.642%   $251.9244   $251.92   $251.90   $251.90  
  Purchase #4 $148.28   5.598%   $156.5807   $156.58   $156.60   $156.60  
  Purchase #5 $113.97   5.628%   $120.3842   $120.38   $120.40   $120.40  
  Purchase #6 $233.99   11.252%   $260.3186   $260.32   $260.30   $260.30  
  Purchase #7 $113.46   7.471%   $121.9366   $121.94   $121.95   $121.90  
  7 purchase totals = $1,034.70       $1,132.1102   $1,132.10   $1,132.10   $1,132.00