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 $82.35   13.393%   $93.3791   $93.38   $93.40   $93.40  
  Purchase #2 $36.98   10.424%   $40.8348   $40.83   $40.85   $40.80  
  Purchase #3 $68.72   7.122%   $73.6142   $73.61   $73.60   $73.60  
  Purchase #4 $67.83   10.675%   $75.0709   $75.07   $75.05   $75.10  
  Purchase #5 $132.36   9.596%   $145.0613   $145.06   $145.05   $145.10  
  Purchase #6 $189.77   4.140%   $197.6265   $197.63   $197.65   $197.60  
  Purchase #7 $131.25   9.309%   $143.4681   $143.47   $143.45   $143.50  
  7 purchase totals = $709.26       $769.0549   $769.05   $769.05   $769.10