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 $68.83   13.233%   $77.9383   $77.94   $77.95   $77.90  
  Purchase #2 $229.53   5.104%   $241.2452   $241.25   $241.25   $241.20  
  Purchase #3 $82.31   6.244%   $87.4494   $87.45   $87.45   $87.40  
  Purchase #4 $73.98   8.634%   $80.3674   $80.37   $80.35   $80.40  
  Purchase #5 $52.70   3.855%   $54.7316   $54.73   $54.75   $54.70  
  Purchase #6 $104.68   13.376%   $118.682   $118.68   $118.70   $118.70  
  Purchase #7 $249.31   7.277%   $267.4523   $267.45   $267.45   $267.50  
  7 purchase totals = $861.34       $927.8662   $927.87   $927.90   $927.80