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 $203.74   3.193%   $210.2454   $210.25   $210.25   $210.20  
  Purchase #2 $104.98   8.148%   $113.5338   $113.53   $113.55   $113.50  
  Purchase #3 $64.88   10.295%   $71.5594   $71.56   $71.55   $71.60  
  Purchase #4 $55.41   4.247%   $57.7633   $57.76   $57.75   $57.80  
  Purchase #5 $183.34   3.530%   $189.8119   $189.81   $189.80   $189.80  
  Purchase #6 $165.43   11.432%   $184.342   $184.34   $184.35   $184.30  
  Purchase #7 $70.77   8.155%   $76.5413   $76.54   $76.55   $76.50  
  7 purchase totals = $848.55       $903.7971   $903.79   $903.80   $903.70