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 $40.83   7.292%   $43.8073   $43.81   $43.80   $43.80  
  Purchase #2 $106.96   10.322%   $118.0004   $118.00   $118.00   $118.00  
  Purchase #3 $76.89   10.795%   $85.1903   $85.19   $85.20   $85.20  
  Purchase #4 $74.46   9.468%   $81.5099   $81.51   $81.50   $81.50  
  Purchase #5 $59.70   8.684%   $64.8843   $64.88   $64.90   $64.90  
  Purchase #6 $146.36   10.188%   $161.2712   $161.27   $161.25   $161.30  
  Purchase #7 $65.58   6.610%   $69.9148   $69.91   $69.90   $69.90  
  7 purchase totals = $570.78       $624.5782   $624.57   $624.55   $624.60