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 $23.34   9.758%   $25.6175   $25.62   $25.60   $25.60  
  Purchase #2 $230.85   3.514%   $238.9621   $238.96   $238.95   $239.00  
  Purchase #3 $56.46   8.580%   $61.3043   $61.30   $61.30   $61.30  
  Purchase #4 $165.39   7.540%   $177.8604   $177.86   $177.85   $177.90  
  Purchase #5 $210.27   11.215%   $233.8518   $233.85   $233.85   $233.90  
  Purchase #6 $18.64   10.162%   $20.5342   $20.53   $20.55   $20.50  
  Purchase #7 $191.48   7.750%   $206.3197   $206.32   $206.30   $206.30  
  7 purchase totals = $896.43       $964.4500   $964.44   $964.40   $964.50