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 $238.79   11.161%   $265.4414   $265.44   $265.45   $265.40  
  Purchase #2 $243.76   9.130%   $266.0153   $266.02   $266.00   $266.00  
  Purchase #3 $245.27   13.410%   $278.1607   $278.16   $278.15   $278.20  
  Purchase #4 $76.93   9.813%   $84.4791   $84.48   $84.50   $84.50  
  Purchase #5 $192.84   5.593%   $203.6255   $203.63   $203.65   $203.60  
  Purchase #6 $56.92   13.605%   $64.664   $64.66   $64.65   $64.70  
  Purchase #7 $245.36   9.346%   $268.2913   $268.29   $268.30   $268.30  
  7 purchase totals = $1,299.87       $1,430.6773   $1,430.68   $1,430.70   $1,430.70