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 $44.92   10.683%   $49.7188   $49.72   $49.70   $49.70  
  Purchase #2 $164.29   13.835%   $187.0195   $187.02   $187.00   $187.00  
  Purchase #3 $194.25   5.851%   $205.6156   $205.62   $205.60   $205.60  
  Purchase #4 $104.97   11.828%   $117.3859   $117.39   $117.40   $117.40  
  Purchase #5 $219.95   13.833%   $250.3757   $250.38   $250.40   $250.40  
  Purchase #6 $90.95   5.715%   $96.1478   $96.15   $96.15   $96.10  
  Purchase #7 $142.67   8.281%   $154.4845   $154.48   $154.50   $154.50  
  7 purchase totals = $962.00       $1,060.7478   $1,060.76   $1,060.75   $1,060.70