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 $41.59   6.217%   $44.1757   $44.18   $44.20   $44.20  
  Purchase #2 $46.74   10.650%   $51.7178   $51.72   $51.70   $51.70  
  Purchase #3 $88.91   3.573%   $92.0868   $92.09   $92.10   $92.10  
  Purchase #4 $8.39   5.813%   $8.8777   $8.88   $8.90   $8.90  
  Purchase #5 $88.71   10.227%   $97.7824   $97.78   $97.80   $97.80  
  Purchase #6 $159.79   10.427%   $176.4513   $176.45   $176.45   $176.50  
  Purchase #7 $238.63   12.190%   $267.719   $267.72   $267.70   $267.70  
  7 purchase totals = $672.76       $738.8107   $738.82   $738.85   $738.90