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 $90.87   3.731%   $94.2604   $94.26   $94.25   $94.30  
  Purchase #2 $228.87   5.456%   $241.3571   $241.36   $241.35   $241.40  
  Purchase #3 $85.55   8.205%   $92.5694   $92.57   $92.55   $92.60  
  Purchase #4 $166.54   7.619%   $179.2287   $179.23   $179.25   $179.20  
  Purchase #5 $47.45   11.762%   $53.0311   $53.03   $53.05   $53.00  
  Purchase #6 $99.44   13.788%   $113.1508   $113.15   $113.15   $113.20  
  Purchase #7 $158.89   7.702%   $171.1277   $171.13   $171.15   $171.10  
  7 purchase totals = $877.61       $944.7252   $944.73   $944.75   $944.80