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 $54.43   7.749%   $58.6478   $58.65   $58.65   $58.60  
  Purchase #2 $215.29   3.872%   $223.626   $223.63   $223.65   $223.60  
  Purchase #3 $71.51   7.812%   $77.0964   $77.10   $77.10   $77.10  
  Purchase #4 $179.76   7.575%   $193.3768   $193.38   $193.40   $193.40  
  Purchase #5 $14.74   5.181%   $15.5037   $15.50   $15.50   $15.50  
  Purchase #6 $36.97   11.712%   $41.2999   $41.30   $41.30   $41.30  
  Purchase #7 $48.72   8.823%   $53.0186   $53.02   $53.00   $53.00  
  7 purchase totals = $621.42       $662.5692   $662.58   $662.60   $662.50