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 $46.97   10.566%   $51.9329   $51.93   $51.95   $51.90  
  Purchase #2 $20.30   12.414%   $22.82   $22.82   $22.80   $22.80  
  Purchase #3 $60.95   13.809%   $69.3666   $69.37   $69.35   $69.40  
  Purchase #4 $248.77   6.806%   $265.7013   $265.70   $265.70   $265.70  
  Purchase #5 $207.83   13.268%   $235.4049   $235.40   $235.40   $235.40  
  Purchase #6 $195.92   7.365%   $210.3495   $210.35   $210.35   $210.30  
  Purchase #7 $51.49   6.475%   $54.824   $54.82   $54.80   $54.80  
  7 purchase totals = $832.23       $910.3992   $910.39   $910.35   $910.30