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 $48.29   6.699%   $51.5249   $51.52   $51.50   $51.50  
  Purchase #2 $219.83   13.381%   $249.2455   $249.25   $249.25   $249.20  
  Purchase #3 $212.26   13.437%   $240.7814   $240.78   $240.80   $240.80  
  Purchase #4 $58.41   8.131%   $63.1593   $63.16   $63.15   $63.20  
  Purchase #5 $214.52   7.543%   $230.7012   $230.70   $230.70   $230.70  
  Purchase #6 $157.61   12.135%   $176.736   $176.74   $176.75   $176.70  
  Purchase #7 $235.92   3.725%   $244.708   $244.71   $244.70   $244.70  
  7 purchase totals = $1,146.84       $1,256.8563   $1,256.86   $1,256.85   $1,256.80