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 $87.33   13.284%   $98.9309   $98.93   $98.95   $98.90  
  Purchase #2 $105.88   11.111%   $117.6443   $117.64   $117.65   $117.60  
  Purchase #3 $195.29   4.825%   $204.7127   $204.71   $204.70   $204.70  
  Purchase #4 $58.82   11.633%   $65.6625   $65.66   $65.65   $65.70  
  Purchase #5 $98.39   7.814%   $106.0782   $106.08   $106.10   $106.10  
  Purchase #6 $37.89   11.524%   $42.2564   $42.26   $42.25   $42.30  
  Purchase #7 $180.39   8.516%   $195.752   $195.75   $195.75   $195.80  
  7 purchase totals = $763.99       $831.0370   $831.03   $831.05   $831.10