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 $67.61   12.578%   $76.114   $76.11   $76.10   $76.10  
  Purchase #2 $47.43   3.595%   $49.1351   $49.14   $49.15   $49.10  
  Purchase #3 $188.71   7.302%   $202.4896   $202.49   $202.50   $202.50  
  Purchase #4 $123.55   8.267%   $133.7639   $133.76   $133.75   $133.80  
  Purchase #5 $216.96   5.685%   $229.2942   $229.29   $229.30   $229.30  
  Purchase #6 $26.93   6.169%   $28.5913   $28.59   $28.60   $28.60  
  Purchase #7 $167.53   6.190%   $177.9001   $177.90   $177.90   $177.90  
  7 purchase totals = $838.72       $897.2882   $897.28   $897.30   $897.30