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 $243.97   13.102%   $275.9349   $275.93   $275.95   $275.90  
  Purchase #2 $71.29   7.196%   $76.42   $76.42   $76.40   $76.40  
  Purchase #3 $146.81   8.644%   $159.5003   $159.50   $159.50   $159.50  
  Purchase #4 $53.47   10.169%   $58.9074   $58.91   $58.90   $58.90  
  Purchase #5 $109.27   5.523%   $115.305   $115.31   $115.30   $115.30  
  Purchase #6 $214.98   11.761%   $240.2638   $240.26   $240.25   $240.30  
  Purchase #7 $23.73   3.521%   $24.5655   $24.57   $24.55   $24.60  
  7 purchase totals = $863.52       $950.8969   $950.90   $950.85   $950.90