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 $121.59   10.151%   $133.9326   $133.93   $133.95   $133.90  
  Purchase #2 $179.82   8.415%   $194.9519   $194.95   $194.95   $195.00  
  Purchase #3 $82.83   7.802%   $89.2924   $89.29   $89.30   $89.30  
  Purchase #4 $164.37   7.815%   $177.2155   $177.22   $177.20   $177.20  
  Purchase #5 $23.60   6.491%   $25.1319   $25.13   $25.15   $25.10  
  Purchase #6 $122.79   8.197%   $132.8551   $132.86   $132.85   $132.90  
  Purchase #7 $190.26   10.189%   $209.6456   $209.65   $209.65   $209.60  
  7 purchase totals = $885.26       $963.0250   $963.03   $963.05   $963.00