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 $192.38   5.783%   $203.5053   $203.51   $203.50   $203.50  
  Purchase #2 $59.44   8.859%   $64.7058   $64.71   $64.70   $64.70  
  Purchase #3 $141.89   3.527%   $146.8945   $146.89   $146.90   $146.90  
  Purchase #4 $166.81   11.849%   $186.5753   $186.58   $186.60   $186.60  
  Purchase #5 $226.60   8.102%   $244.9591   $244.96   $244.95   $245.00  
  Purchase #6 $213.78   11.498%   $238.3604   $238.36   $238.35   $238.40  
  Purchase #7 $148.26   8.453%   $160.7924   $160.79   $160.80   $160.80  
  7 purchase totals = $1,149.16       $1,245.7928   $1,245.80   $1,245.80   $1,245.90