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 $57.57   7.849%   $62.0887   $62.09   $62.10   $62.10  
  Purchase #2 $67.84   5.680%   $71.6933   $71.69   $71.70   $71.70  
  Purchase #3 $152.58   6.579%   $162.6182   $162.62   $162.60   $162.60  
  Purchase #4 $95.49   3.536%   $98.8665   $98.87   $98.85   $98.90  
  Purchase #5 $96.80   10.303%   $106.7733   $106.77   $106.75   $106.80  
  Purchase #6 $244.79   6.216%   $260.0061   $260.01   $260.00   $260.00  
  Purchase #7 $98.98   8.370%   $107.2646   $107.26   $107.25   $107.30  
  7 purchase totals = $814.05       $869.3107   $869.31   $869.25   $869.40