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 $194.52   10.683%   $215.3006   $215.30   $215.30   $215.30  
  Purchase #2 $241.82   7.498%   $259.9517   $259.95   $259.95   $260.00  
  Purchase #3 $244.34   13.756%   $277.9514   $277.95   $277.95   $278.00  
  Purchase #4 $68.32   6.162%   $72.5299   $72.53   $72.55   $72.50  
  Purchase #5 $231.88   7.562%   $249.4148   $249.41   $249.40   $249.40  
  Purchase #6 $156.83   10.685%   $173.5873   $173.59   $173.60   $173.60  
  Purchase #7 $189.99   10.244%   $209.4526   $209.45   $209.45   $209.50  
  7 purchase totals = $1,327.70       $1,458.1883   $1,458.18   $1,458.20   $1,458.30