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 $46.82   8.165%   $50.6429   $50.64   $50.65   $50.60  
  Purchase #2 $135.44   9.561%   $148.3894   $148.39   $148.40   $148.40  
  Purchase #3 $98.44   9.456%   $107.7485   $107.75   $107.75   $107.70  
  Purchase #4 $174.28   8.637%   $189.3326   $189.33   $189.35   $189.30  
  Purchase #5 $195.65   13.372%   $221.8123   $221.81   $221.80   $221.80  
  Purchase #6 $214.37   8.699%   $233.018   $233.02   $233.00   $233.00  
  Purchase #7 $15.62   13.148%   $17.6737   $17.67   $17.65   $17.70  
  7 purchase totals = $880.62       $968.6174   $968.61   $968.60   $968.50