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 $98.46   6.396%   $104.7575   $104.76   $104.75   $104.80  
  Purchase #2 $144.68   6.808%   $154.5298   $154.53   $154.55   $154.50  
  Purchase #3 $90.33   6.814%   $96.4851   $96.49   $96.50   $96.50  
  Purchase #4 $210.32   3.328%   $217.3194   $217.32   $217.30   $217.30  
  Purchase #5 $160.60   6.135%   $170.4528   $170.45   $170.45   $170.50  
  Purchase #6 $231.34   11.693%   $258.3906   $258.39   $258.40   $258.40  
  Purchase #7 $233.38   10.485%   $257.8499   $257.85   $257.85   $257.80  
  7 purchase totals = $1,169.11       $1,259.7851   $1,259.79   $1,259.80   $1,259.80