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 $75.73   13.391%   $85.871   $85.87   $85.85   $85.90  
  Purchase #2 $165.57   5.292%   $174.332   $174.33   $174.35   $174.30  
  Purchase #3 $91.99   10.863%   $101.9829   $101.98   $102.00   $102.00  
  Purchase #4 $60.78   11.610%   $67.8366   $67.84   $67.85   $67.80  
  Purchase #5 $172.88   3.405%   $178.7666   $178.77   $178.75   $178.80  
  Purchase #6 $53.79   7.862%   $58.019   $58.02   $58.00   $58.00  
  Purchase #7 $112.39   3.855%   $116.7226   $116.72   $116.70   $116.70  
  7 purchase totals = $733.13       $783.5307   $783.53   $783.50   $783.50