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 $212.84   12.644%   $239.7515   $239.75   $239.75   $239.80  
  Purchase #2 $242.73   9.771%   $266.4471   $266.45   $266.45   $266.40  
  Purchase #3 $55.94   9.605%   $61.313   $61.31   $61.30   $61.30  
  Purchase #4 $168.46   4.602%   $176.2125   $176.21   $176.20   $176.20  
  Purchase #5 $156.84   8.863%   $170.7407   $170.74   $170.75   $170.70  
  Purchase #6 $127.47   12.143%   $142.9487   $142.95   $142.95   $142.90  
  Purchase #7 $82.84   3.347%   $85.6127   $85.61   $85.60   $85.60  
  7 purchase totals = $1,047.12       $1,143.0262   $1,143.02   $1,143.00   $1,142.90