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 $84.79   13.278%   $96.0484   $96.05   $96.05   $96.00  
  Purchase #2 $229.73   10.282%   $253.3508   $253.35   $253.35   $253.40  
  Purchase #3 $175.49   13.337%   $198.8951   $198.90   $198.90   $198.90  
  Purchase #4 $60.51   7.113%   $64.8141   $64.81   $64.80   $64.80  
  Purchase #5 $117.97   9.798%   $129.5287   $129.53   $129.55   $129.50  
  Purchase #6 $108.54   8.426%   $117.6856   $117.69   $117.70   $117.70  
  Purchase #7 $29.67   13.319%   $33.6217   $33.62   $33.60   $33.60  
  7 purchase totals = $806.70       $893.9444   $893.95   $893.95   $893.90