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 $58.49   10.226%   $64.4712   $64.47   $64.45   $64.50  
  Purchase #2 $160.73   8.832%   $174.9257   $174.93   $174.95   $174.90  
  Purchase #3 $167.81   7.129%   $179.7732   $179.77   $179.75   $179.80  
  Purchase #4 $188.94   10.798%   $209.3417   $209.34   $209.35   $209.30  
  Purchase #5 $186.31   4.758%   $195.1746   $195.17   $195.15   $195.20  
  Purchase #6 $195.56   10.123%   $215.3565   $215.36   $215.35   $215.40  
  Purchase #7 $30.32   13.139%   $34.3037   $34.30   $34.30   $34.30  
  7 purchase totals = $988.16       $1,073.3466   $1,073.34   $1,073.30   $1,073.40