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 $218.53   8.262%   $236.5849   $236.58   $236.60   $236.60  
  Purchase #2 $243.48   4.712%   $254.9528   $254.95   $254.95   $255.00  
  Purchase #3 $226.74   7.873%   $244.5912   $244.59   $244.60   $244.60  
  Purchase #4 $61.29   4.419%   $63.9984   $64.00   $64.00   $64.00  
  Purchase #5 $177.53   3.281%   $183.3548   $183.35   $183.35   $183.40  
  Purchase #6 $213.34   11.422%   $237.7077   $237.71   $237.70   $237.70  
  Purchase #7 $93.60   5.192%   $98.4597   $98.46   $98.45   $98.50  
  7 purchase totals = $1,234.51       $1,319.6495   $1,319.64   $1,319.65   $1,319.80