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 $58.53   9.259%   $63.9493   $63.95   $63.95   $63.90  
  Purchase #2 $232.47   7.518%   $249.9471   $249.95   $249.95   $249.90  
  Purchase #3 $89.80   4.567%   $93.9012   $93.90   $93.90   $93.90  
  Purchase #4 $104.76   10.239%   $115.4864   $115.49   $115.50   $115.50  
  Purchase #5 $235.82   6.469%   $251.0752   $251.08   $251.10   $251.10  
  Purchase #6 $24.58   4.395%   $25.6603   $25.66   $25.65   $25.70  
  Purchase #7 $115.95   13.314%   $131.3876   $131.39   $131.40   $131.40  
  7 purchase totals = $861.91       $931.4071   $931.42   $931.45   $931.40