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 $53.41   11.179%   $59.3807   $59.38   $59.40   $59.40  
  Purchase #2 $218.66   7.147%   $234.2876   $234.29   $234.30   $234.30  
  Purchase #3 $216.90   11.270%   $241.3446   $241.34   $241.35   $241.30  
  Purchase #4 $97.74   10.206%   $107.7153   $107.72   $107.70   $107.70  
  Purchase #5 $93.74   9.852%   $102.9753   $102.98   $103.00   $103.00  
  Purchase #6 $153.37   13.435%   $173.9753   $173.98   $174.00   $174.00  
  Purchase #7 $25.29   10.632%   $27.9788   $27.98   $28.00   $28.00  
  7 purchase totals = $859.11       $947.6576   $947.67   $947.75   $947.70