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 $112.39   12.544%   $126.4882   $126.49   $126.50   $126.50  
  Purchase #2 $240.26   7.307%   $257.8158   $257.82   $257.80   $257.80  
  Purchase #3 $49.64   11.123%   $55.1615   $55.16   $55.15   $55.20  
  Purchase #4 $168.53   11.487%   $187.889   $187.89   $187.90   $187.90  
  Purchase #5 $147.49   13.323%   $167.1401   $167.14   $167.15   $167.10  
  Purchase #6 $215.33   9.670%   $236.1524   $236.15   $236.15   $236.20  
  Purchase #7 $27.76   5.261%   $29.2205   $29.22   $29.20   $29.20  
  7 purchase totals = $961.40       $1,059.8675   $1,059.87   $1,059.85   $1,059.90