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 $67.44   11.672%   $75.3116   $75.31   $75.30   $75.30  
  Purchase #2 $163.50   7.867%   $176.3625   $176.36   $176.35   $176.40  
  Purchase #3 $60.96   12.251%   $68.4282   $68.43   $68.45   $68.40  
  Purchase #4 $50.64   7.293%   $54.3332   $54.33   $54.35   $54.30  
  Purchase #5 $76.85   10.557%   $84.9631   $84.96   $84.95   $85.00  
  Purchase #6 $250.48   6.486%   $266.7261   $266.73   $266.75   $266.70  
  Purchase #7 $157.71   9.189%   $172.202   $172.20   $172.20   $172.20  
  7 purchase totals = $827.58       $898.3267   $898.32   $898.35   $898.30