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 $122.82   9.323%   $134.2705   $134.27   $134.25   $134.30  
  Purchase #2 $20.74   5.167%   $21.8116   $21.81   $21.80   $21.80  
  Purchase #3 $201.95   8.667%   $219.453   $219.45   $219.45   $219.50  
  Purchase #4 $95.48   8.871%   $103.95   $103.95   $103.95   $104.00  
  Purchase #5 $249.96   12.808%   $281.9749   $281.97   $281.95   $282.00  
  Purchase #6 $8.56   4.787%   $8.9698   $8.97   $8.95   $9.00  
  Purchase #7 $157.44   11.246%   $175.1457   $175.15   $175.15   $175.10  
  7 purchase totals = $856.95       $945.5755   $945.57   $945.50   $945.70