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 $246.43   5.802%   $260.7279   $260.73   $260.75   $260.70  
  Purchase #2 $210.53   4.670%   $220.3618   $220.36   $220.35   $220.40  
  Purchase #3 $206.67   8.358%   $223.9435   $223.94   $223.95   $223.90  
  Purchase #4 $110.74   13.631%   $125.835   $125.84   $125.85   $125.80  
  Purchase #5 $200.80   4.721%   $210.2798   $210.28   $210.30   $210.30  
  Purchase #6 $68.26   10.130%   $75.1747   $75.17   $75.15   $75.20  
  Purchase #7 $147.28   4.854%   $154.429   $154.43   $154.45   $154.40  
  7 purchase totals = $1,190.71       $1,270.7517   $1,270.75   $1,270.80   $1,270.70