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 $87.36   8.564%   $94.8415   $94.84   $94.85   $94.80  
  Purchase #2 $245.99   12.483%   $276.6969   $276.70   $276.70   $276.70  
  Purchase #3 $28.92   8.206%   $31.2932   $31.29   $31.30   $31.30  
  Purchase #4 $200.65   5.799%   $212.2857   $212.29   $212.30   $212.30  
  Purchase #5 $227.51   9.627%   $249.4124   $249.41   $249.40   $249.40  
  Purchase #6 $25.51   4.830%   $26.7421   $26.74   $26.75   $26.70  
  Purchase #7 $15.82   10.383%   $17.4626   $17.46   $17.45   $17.50  
  7 purchase totals = $831.76       $908.7344   $908.73   $908.75   $908.70