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 $231.30   12.758%   $260.8093   $260.81   $260.80   $260.80  
  Purchase #2 $91.27   5.288%   $96.0964   $96.10   $96.10   $96.10  
  Purchase #3 $165.46   6.473%   $176.1702   $176.17   $176.15   $176.20  
  Purchase #4 $115.37   4.439%   $120.4913   $120.49   $120.50   $120.50  
  Purchase #5 $122.70   5.292%   $129.1933   $129.19   $129.20   $129.20  
  Purchase #6 $80.86   4.479%   $84.4817   $84.48   $84.50   $84.50  
  Purchase #7 $105.90   12.113%   $118.7277   $118.73   $118.75   $118.70  
  7 purchase totals = $912.86       $985.9699   $985.97   $986.00   $986.00