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 $119.95   13.156%   $135.7306   $135.73   $135.75   $135.70  
  Purchase #2 $64.66   6.555%   $68.8985   $68.90   $68.90   $68.90  
  Purchase #3 $84.49   5.726%   $89.3279   $89.33   $89.35   $89.30  
  Purchase #4 $24.32   9.616%   $26.6586   $26.66   $26.65   $26.70  
  Purchase #5 $154.86   12.718%   $174.5551   $174.56   $174.55   $174.60  
  Purchase #6 $11.26   10.191%   $12.4075   $12.41   $12.40   $12.40  
  Purchase #7 $209.87   7.341%   $225.2766   $225.28   $225.30   $225.30  
  7 purchase totals = $669.41       $732.8548   $732.87   $732.90   $732.90