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 $67.46   12.201%   $75.6908   $75.69   $75.70   $75.70  
  Purchase #2 $119.76   12.683%   $134.9492   $134.95   $134.95   $134.90  
  Purchase #3 $36.53   9.644%   $40.053   $40.05   $40.05   $40.10  
  Purchase #4 $96.44   7.420%   $103.5958   $103.60   $103.60   $103.60  
  Purchase #5 $182.86   6.566%   $194.8666   $194.87   $194.85   $194.90  
  Purchase #6 $49.52   8.544%   $53.751   $53.75   $53.75   $53.80  
  Purchase #7 $103.95   3.567%   $107.6579   $107.66   $107.65   $107.70  
  7 purchase totals = $656.52       $710.5643   $710.57   $710.55   $710.70