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 $180.42   13.435%   $204.6594   $204.66   $204.65   $204.70  
  Purchase #2 $32.77   5.872%   $34.6943   $34.69   $34.70   $34.70  
  Purchase #3 $217.98   12.447%   $245.112   $245.11   $245.10   $245.10  
  Purchase #4 $24.57   6.591%   $26.1894   $26.19   $26.20   $26.20  
  Purchase #5 $50.38   8.662%   $54.7439   $54.74   $54.75   $54.70  
  Purchase #6 $169.88   10.664%   $187.996   $188.00   $188.00   $188.00  
  Purchase #7 $83.50   11.174%   $92.8303   $92.83   $92.85   $92.80  
  7 purchase totals = $759.50       $846.2253   $846.22   $846.25   $846.20