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 $239.74   10.740%   $265.4881   $265.49   $265.50   $265.50  
  Purchase #2 $106.85   12.434%   $120.1357   $120.14   $120.15   $120.10  
  Purchase #3 $26.37   5.171%   $27.7336   $27.73   $27.75   $27.70  
  Purchase #4 $50.96   4.554%   $53.2807   $53.28   $53.30   $53.30  
  Purchase #5 $119.78   12.293%   $134.5046   $134.50   $134.50   $134.50  
  Purchase #6 $179.34   4.234%   $186.9333   $186.93   $186.95   $186.90  
  Purchase #7 $150.58   3.602%   $156.0039   $156.00   $156.00   $156.00  
  7 purchase totals = $873.62       $944.0799   $944.07   $944.15   $944.00