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 $63.46   12.483%   $71.3817   $71.38   $71.40   $71.40  
  Purchase #2 $173.72   10.308%   $191.6271   $191.63   $191.65   $191.60  
  Purchase #3 $244.48   7.874%   $263.7304   $263.73   $263.75   $263.70  
  Purchase #4 $148.47   10.801%   $164.5062   $164.51   $164.50   $164.50  
  Purchase #5 $101.58   5.667%   $107.3365   $107.34   $107.35   $107.30  
  Purchase #6 $223.27   9.729%   $244.9919   $244.99   $245.00   $245.00  
  Purchase #7 $249.40   5.151%   $262.2466   $262.25   $262.25   $262.20  
  7 purchase totals = $1,204.38       $1,305.8204   $1,305.83   $1,305.90   $1,305.70