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 $44.93   8.626%   $48.8057   $48.81   $48.80   $48.80  
  Purchase #2 $215.70   9.295%   $235.7493   $235.75   $235.75   $235.70  
  Purchase #3 $249.33   4.168%   $259.7221   $259.72   $259.70   $259.70  
  Purchase #4 $175.99   5.511%   $185.6888   $185.69   $185.70   $185.70  
  Purchase #5 $44.51   10.853%   $49.3407   $49.34   $49.35   $49.30  
  Purchase #6 $94.74   6.476%   $100.8754   $100.88   $100.90   $100.90  
  Purchase #7 $110.82   10.617%   $122.5858   $122.59   $122.60   $122.60  
  7 purchase totals = $936.02       $1,002.7678   $1,002.78   $1,002.80   $1,002.70