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 $250.46   5.706%   $264.7512   $264.75   $264.75   $264.80  
  Purchase #2 $229.95   10.655%   $254.4512   $254.45   $254.45   $254.50  
  Purchase #3 $200.80   6.207%   $213.2637   $213.26   $213.25   $213.30  
  Purchase #4 $206.96   12.357%   $232.534   $232.53   $232.55   $232.50  
  Purchase #5 $152.27   13.815%   $173.3061   $173.31   $173.30   $173.30  
  Purchase #6 $226.59   3.455%   $234.4187   $234.42   $234.40   $234.40  
  Purchase #7 $23.83   3.731%   $24.7191   $24.72   $24.70   $24.70  
  7 purchase totals = $1,290.86       $1,397.4440   $1,397.44   $1,397.40   $1,397.50