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 $59.66   11.596%   $66.5782   $66.58   $66.60   $66.60  
  Purchase #2 $215.31   8.774%   $234.2013   $234.20   $234.20   $234.20  
  Purchase #3 $20.28   12.327%   $22.7799   $22.78   $22.80   $22.80  
  Purchase #4 $165.98   6.388%   $176.5828   $176.58   $176.60   $176.60  
  Purchase #5 $6.73   8.369%   $7.2932   $7.29   $7.30   $7.30  
  Purchase #6 $150.35   3.692%   $155.9009   $155.90   $155.90   $155.90  
  Purchase #7 $221.30   12.200%   $248.2986   $248.30   $248.30   $248.30  
  7 purchase totals = $839.61       $911.6349   $911.63   $911.70   $911.70