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 $116.96   6.291%   $124.318   $124.32   $124.30   $124.30  
  Purchase #2 $54.80   6.650%   $58.4442   $58.44   $58.45   $58.40  
  Purchase #3 $129.60   4.246%   $135.1028   $135.10   $135.10   $135.10  
  Purchase #4 $41.42   12.134%   $46.4459   $46.45   $46.45   $46.40  
  Purchase #5 $246.75   12.740%   $278.186   $278.19   $278.20   $278.20  
  Purchase #6 $88.57   3.391%   $91.5734   $91.57   $91.55   $91.60  
  Purchase #7 $154.65   4.706%   $161.9278   $161.93   $161.95   $161.90  
  7 purchase totals = $832.75       $895.9981   $896.00   $896.00   $895.90