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 $249.74   10.818%   $276.7569   $276.76   $276.75   $276.80  
  Purchase #2 $106.99   11.767%   $119.5795   $119.58   $119.60   $119.60  
  Purchase #3 $26.31   10.858%   $29.1667   $29.17   $29.15   $29.20  
  Purchase #4 $104.46   12.700%   $117.7264   $117.73   $117.75   $117.70  
  Purchase #5 $183.31   7.845%   $197.6907   $197.69   $197.70   $197.70  
  Purchase #6 $11.62   7.788%   $12.525   $12.53   $12.55   $12.50  
  Purchase #7 $90.25   5.252%   $94.9899   $94.99   $95.00   $95.00  
  7 purchase totals = $772.68       $848.4351   $848.45   $848.50   $848.50