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 $144.40   11.144%   $160.4919   $160.49   $160.50   $160.50  
  Purchase #2 $54.97   12.194%   $61.673   $61.67   $61.65   $61.70  
  Purchase #3 $245.38   12.656%   $276.4353   $276.44   $276.45   $276.40  
  Purchase #4 $235.59   11.662%   $263.0645   $263.06   $263.05   $263.10  
  Purchase #5 $164.97   10.610%   $182.4733   $182.47   $182.45   $182.50  
  Purchase #6 $220.65   7.373%   $236.9185   $236.92   $236.90   $236.90  
  Purchase #7 $189.42   7.177%   $203.0147   $203.01   $203.00   $203.00  
  7 purchase totals = $1,255.38       $1,384.0712   $1,384.06   $1,384.00   $1,384.10