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 $213.65   6.502%   $227.5415   $227.54   $227.55   $227.50  
  Purchase #2 $178.98   7.176%   $191.8236   $191.82   $191.80   $191.80  
  Purchase #3 $49.34   12.733%   $55.6225   $55.62   $55.60   $55.60  
  Purchase #4 $245.71   4.723%   $257.3149   $257.31   $257.30   $257.30  
  Purchase #5 $242.77   11.403%   $270.4531   $270.45   $270.45   $270.50  
  Purchase #6 $169.64   7.485%   $182.3376   $182.34   $182.35   $182.30  
  Purchase #7 $22.52   9.855%   $24.7393   $24.74   $24.75   $24.70  
  7 purchase totals = $1,122.61       $1,209.8325   $1,209.82   $1,209.80   $1,209.70