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 $126.28   11.770%   $141.1432   $141.14   $141.15   $141.10  
  Purchase #2 $95.54   13.231%   $108.1809   $108.18   $108.20   $108.20  
  Purchase #3 $134.56   7.195%   $144.2416   $144.24   $144.25   $144.20  
  Purchase #4 $245.73   6.726%   $262.2578   $262.26   $262.25   $262.30  
  Purchase #5 $193.37   4.620%   $202.3037   $202.30   $202.30   $202.30  
  Purchase #6 $129.73   10.690%   $143.5981   $143.60   $143.60   $143.60  
  Purchase #7 $56.27   10.730%   $62.3078   $62.31   $62.30   $62.30  
  7 purchase totals = $981.48       $1,064.0331   $1,064.03   $1,064.05   $1,064.00