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 $217.83   9.256%   $237.9923   $237.99   $238.00   $238.00  
  Purchase #2 $153.56   11.331%   $170.9599   $170.96   $170.95   $171.00  
  Purchase #3 $17.51   9.623%   $19.195   $19.20   $19.20   $19.20  
  Purchase #4 $75.66   11.861%   $84.634   $84.63   $84.65   $84.60  
  Purchase #5 $162.31   5.648%   $171.4773   $171.48   $171.50   $171.50  
  Purchase #6 $64.71   11.396%   $72.0844   $72.08   $72.10   $72.10  
  Purchase #7 $14.61   8.694%   $15.8802   $15.88   $15.90   $15.90  
  7 purchase totals = $706.19       $772.2231   $772.22   $772.30   $772.30