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 $239.95   10.334%   $264.7464   $264.75   $264.75   $264.70  
  Purchase #2 $99.78   13.123%   $112.8741   $112.87   $112.85   $112.90  
  Purchase #3 $100.67   10.761%   $111.5031   $111.50   $111.50   $111.50  
  Purchase #4 $68.75   6.147%   $72.9761   $72.98   $73.00   $73.00  
  Purchase #5 $68.30   8.450%   $74.0714   $74.07   $74.05   $74.10  
  Purchase #6 $21.82   3.149%   $22.5071   $22.51   $22.50   $22.50  
  Purchase #7 $241.36   9.192%   $263.5458   $263.55   $263.55   $263.50  
  7 purchase totals = $840.63       $922.2240   $922.23   $922.20   $922.20