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 $183.94   5.869%   $194.7354   $194.74   $194.75   $194.70  
  Purchase #2 $216.78   12.784%   $244.4932   $244.49   $244.50   $244.50  
  Purchase #3 $118.72   4.233%   $123.7454   $123.75   $123.75   $123.70  
  Purchase #4 $146.86   3.734%   $152.3438   $152.34   $152.35   $152.30  
  Purchase #5 $101.97   5.779%   $107.8628   $107.86   $107.85   $107.90  
  Purchase #6 $197.44   4.298%   $205.926   $205.93   $205.95   $205.90  
  Purchase #7 $193.89   7.861%   $209.1317   $209.13   $209.15   $209.10  
  7 purchase totals = $1,159.60       $1,238.2383   $1,238.24   $1,238.30   $1,238.10