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 $47.39   4.510%   $49.5273   $49.53   $49.55   $49.50  
  Purchase #2 $210.78   10.843%   $233.6349   $233.63   $233.65   $233.60  
  Purchase #3 $228.99   8.204%   $247.7763   $247.78   $247.80   $247.80  
  Purchase #4 $140.33   8.795%   $152.672   $152.67   $152.65   $152.70  
  Purchase #5 $194.73   9.786%   $213.7863   $213.79   $213.80   $213.80  
  Purchase #6 $138.37   10.555%   $152.975   $152.98   $153.00   $153.00  
  Purchase #7 $223.46   12.834%   $252.1389   $252.14   $252.15   $252.10  
  7 purchase totals = $1,184.05       $1,302.5107   $1,302.52   $1,302.60   $1,302.50