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 $236.62   3.543%   $245.0034   $245.00   $245.00   $245.00  
  Purchase #2 $119.38   9.206%   $130.3701   $130.37   $130.35   $130.40  
  Purchase #3 $246.82   4.858%   $258.8105   $258.81   $258.80   $258.80  
  Purchase #4 $72.96   6.645%   $77.8082   $77.81   $77.80   $77.80  
  Purchase #5 $206.92   12.299%   $232.3691   $232.37   $232.35   $232.40  
  Purchase #6 $188.43   3.757%   $195.5093   $195.51   $195.50   $195.50  
  Purchase #7 $166.89   11.858%   $186.6798   $186.68   $186.70   $186.70  
  7 purchase totals = $1,238.02       $1,326.5504   $1,326.55   $1,326.50   $1,326.60