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 $151.89   11.827%   $169.854   $169.85   $169.85   $169.90  
  Purchase #2 $24.58   9.322%   $26.8713   $26.87   $26.85   $26.90  
  Purchase #3 $65.57   11.729%   $73.2607   $73.26   $73.25   $73.30  
  Purchase #4 $188.99   10.142%   $208.1574   $208.16   $208.15   $208.20  
  Purchase #5 $218.54   8.635%   $237.4109   $237.41   $237.40   $237.40  
  Purchase #6 $104.71   4.665%   $109.5947   $109.59   $109.60   $109.60  
  Purchase #7 $181.36   10.784%   $200.9179   $200.92   $200.90   $200.90  
  7 purchase totals = $935.64       $1,026.0669   $1,026.06   $1,026.00   $1,026.20