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 $236.66   4.203%   $246.6068   $246.61   $246.60   $246.60  
  Purchase #2 $213.96   9.757%   $234.8361   $234.84   $234.85   $234.80  
  Purchase #3 $196.44   11.443%   $218.9186   $218.92   $218.90   $218.90  
  Purchase #4 $87.29   3.492%   $90.3382   $90.34   $90.35   $90.30  
  Purchase #5 $27.81   4.240%   $28.9891   $28.99   $29.00   $29.00  
  Purchase #6 $46.87   13.424%   $53.1618   $53.16   $53.15   $53.20  
  Purchase #7 $124.55   8.706%   $135.3933   $135.39   $135.40   $135.40  
  7 purchase totals = $933.58       $1,008.2439   $1,008.25   $1,008.25   $1,008.20