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 $69.61   9.486%   $76.2132   $76.21   $76.20   $76.20  
  Purchase #2 $8.53   4.327%   $8.8991   $8.90   $8.90   $8.90  
  Purchase #3 $184.47   13.866%   $210.0486   $210.05   $210.05   $210.00  
  Purchase #4 $54.63   3.663%   $56.6311   $56.63   $56.65   $56.60  
  Purchase #5 $76.96   7.662%   $82.8567   $82.86   $82.85   $82.90  
  Purchase #6 $152.38   7.358%   $163.5921   $163.59   $163.60   $163.60  
  Purchase #7 $126.41   6.818%   $135.0286   $135.03   $135.05   $135.00  
  7 purchase totals = $672.99       $733.2694   $733.27   $733.30   $733.20