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 $116.67   13.571%   $132.5033   $132.50   $132.50   $132.50  
  Purchase #2 $155.68   6.626%   $165.9954   $166.00   $166.00   $166.00  
  Purchase #3 $100.91   7.830%   $108.8113   $108.81   $108.80   $108.80  
  Purchase #4 $89.62   7.513%   $96.3532   $96.35   $96.35   $96.40  
  Purchase #5 $59.85   9.332%   $65.4352   $65.44   $65.45   $65.40  
  Purchase #6 $166.99   13.266%   $189.1429   $189.14   $189.15   $189.10  
  Purchase #7 $127.63   7.810%   $137.5979   $137.60   $137.60   $137.60  
  7 purchase totals = $817.35       $895.8392   $895.84   $895.85   $895.80