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 $245.41   9.611%   $268.9964   $269.00   $269.00   $269.00  
  Purchase #2 $28.46   11.214%   $31.6515   $31.65   $31.65   $31.70  
  Purchase #3 $195.69   5.545%   $206.541   $206.54   $206.55   $206.50  
  Purchase #4 $103.38   4.869%   $108.4136   $108.41   $108.40   $108.40  
  Purchase #5 $61.94   6.706%   $66.0937   $66.09   $66.10   $66.10  
  Purchase #6 $88.46   9.664%   $97.0088   $97.01   $97.00   $97.00  
  Purchase #7 $36.34   9.260%   $39.7051   $39.71   $39.70   $39.70  
  7 purchase totals = $759.68       $818.4101   $818.41   $818.40   $818.40