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 $12.80   11.637%   $14.2895   $14.29   $14.30   $14.30  
  Purchase #2 $111.73   11.600%   $124.6907   $124.69   $124.70   $124.70  
  Purchase #3 $96.45   13.407%   $109.3811   $109.38   $109.40   $109.40  
  Purchase #4 $150.59   8.151%   $162.8646   $162.86   $162.85   $162.90  
  Purchase #5 $166.81   8.229%   $180.5368   $180.54   $180.55   $180.50  
  Purchase #6 $206.70   5.434%   $217.9321   $217.93   $217.95   $217.90  
  Purchase #7 $216.88   8.292%   $234.8637   $234.86   $234.85   $234.90  
  7 purchase totals = $961.96       $1,044.5585   $1,044.55   $1,044.60   $1,044.60