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 $60.35   11.252%   $67.1406   $67.14   $67.15   $67.10  
  Purchase #2 $113.26   8.458%   $122.8395   $122.84   $122.85   $122.80  
  Purchase #3 $51.88   4.626%   $54.28   $54.28   $54.30   $54.30  
  Purchase #4 $97.28   3.208%   $100.4007   $100.40   $100.40   $100.40  
  Purchase #5 $238.41   13.757%   $271.2081   $271.21   $271.20   $271.20  
  Purchase #6 $66.64   13.667%   $75.7477   $75.75   $75.75   $75.70  
  Purchase #7 $157.96   4.793%   $165.531   $165.53   $165.55   $165.50  
  7 purchase totals = $785.78       $857.1476   $857.15   $857.20   $857.00