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 $56.88   4.811%   $59.6165   $59.62   $59.60   $59.60  
  Purchase #2 $25.81   3.532%   $26.7216   $26.72   $26.70   $26.70  
  Purchase #3 $65.68   7.759%   $70.7761   $70.78   $70.80   $70.80  
  Purchase #4 $100.38   8.255%   $108.6664   $108.67   $108.65   $108.70  
  Purchase #5 $218.68   11.216%   $243.2071   $243.21   $243.20   $243.20  
  Purchase #6 $162.88   4.157%   $169.6509   $169.65   $169.65   $169.70  
  Purchase #7 $74.53   9.666%   $81.7341   $81.73   $81.75   $81.70  
  7 purchase totals = $704.84       $760.3727   $760.38   $760.35   $760.40