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 $57.76   10.871%   $64.0391   $64.04   $64.05   $64.00  
  Purchase #2 $224.98   9.548%   $246.4611   $246.46   $246.45   $246.50  
  Purchase #3 $118.88   12.333%   $133.5415   $133.54   $133.55   $133.50  
  Purchase #4 $213.62   6.157%   $226.7726   $226.77   $226.75   $226.80  
  Purchase #5 $9.38   10.355%   $10.3513   $10.35   $10.35   $10.40  
  Purchase #6 $80.51   4.215%   $83.9035   $83.90   $83.90   $83.90  
  Purchase #7 $229.82   8.242%   $248.7618   $248.76   $248.75   $248.80  
  7 purchase totals = $934.95       $1,013.8309   $1,013.82   $1,013.80   $1,013.90