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 $131.97   7.185%   $141.452   $141.45   $141.45   $141.50  
  Purchase #2 $54.81   13.167%   $62.0268   $62.03   $62.05   $62.00  
  Purchase #3 $228.85   11.265%   $254.63   $254.63   $254.65   $254.60  
  Purchase #4 $221.63   8.198%   $239.7992   $239.80   $239.80   $239.80  
  Purchase #5 $224.39   6.537%   $239.0584   $239.06   $239.05   $239.10  
  Purchase #6 $206.81   13.777%   $235.3022   $235.30   $235.30   $235.30  
  Purchase #7 $51.38   5.136%   $54.0189   $54.02   $54.00   $54.00  
  7 purchase totals = $1,119.84       $1,226.2875   $1,226.29   $1,226.30   $1,226.30