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 $14.98   10.259%   $16.5168   $16.52   $16.50   $16.50  
  Purchase #2 $149.53   8.168%   $161.7436   $161.74   $161.75   $161.70  
  Purchase #3 $20.98   13.479%   $23.8079   $23.81   $23.80   $23.80  
  Purchase #4 $125.48   10.401%   $138.5312   $138.53   $138.55   $138.50  
  Purchase #5 $34.79   4.484%   $36.35   $36.35   $36.35   $36.40  
  Purchase #6 $222.40   7.773%   $239.6872   $239.69   $239.70   $239.70  
  Purchase #7 $144.82   5.520%   $152.8141   $152.81   $152.80   $152.80  
  7 purchase totals = $712.98       $769.4508   $769.45   $769.45   $769.40