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 $87.57   5.788%   $92.6386   $92.64   $92.65   $92.60  
  Purchase #2 $113.96   6.348%   $121.1942   $121.19   $121.20   $121.20  
  Purchase #3 $32.39   12.467%   $36.4281   $36.43   $36.45   $36.40  
  Purchase #4 $185.75   5.791%   $196.5068   $196.51   $196.50   $196.50  
  Purchase #5 $159.48   5.797%   $168.7251   $168.73   $168.75   $168.70  
  Purchase #6 $94.52   4.736%   $98.9965   $99.00   $99.00   $99.00  
  Purchase #7 $13.54   4.223%   $14.1118   $14.11   $14.10   $14.10  
  7 purchase totals = $687.21       $728.6011   $728.61   $728.65   $728.50