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 $90.31   6.316%   $96.014   $96.01   $96.00   $96.00  
  Purchase #2 $127.44   6.677%   $135.9492   $135.95   $135.95   $135.90  
  Purchase #3 $14.28   8.838%   $15.5421   $15.54   $15.55   $15.50  
  Purchase #4 $43.94   7.323%   $47.1577   $47.16   $47.15   $47.20  
  Purchase #5 $52.81   11.332%   $58.7944   $58.79   $58.80   $58.80  
  Purchase #6 $33.66   10.141%   $37.0735   $37.07   $37.05   $37.10  
  Purchase #7 $70.95   7.685%   $76.4025   $76.40   $76.40   $76.40  
  7 purchase totals = $433.39       $466.9334   $466.92   $466.90   $466.90