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 $244.56   8.354%   $264.9905   $264.99   $265.00   $265.00  
  Purchase #2 $128.44   13.793%   $146.1557   $146.16   $146.15   $146.20  
  Purchase #3 $93.91   4.346%   $97.9913   $97.99   $98.00   $98.00  
  Purchase #4 $132.47   9.596%   $145.1818   $145.18   $145.20   $145.20  
  Purchase #5 $51.46   8.266%   $55.7137   $55.71   $55.70   $55.70  
  Purchase #6 $133.84   11.765%   $149.5863   $149.59   $149.60   $149.60  
  Purchase #7 $88.36   4.816%   $92.6154   $92.62   $92.60   $92.60  
  7 purchase totals = $873.04       $952.2347   $952.24   $952.25   $952.30