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 $19.29   8.599%   $20.9487   $20.95   $20.95   $20.90  
  Purchase #2 $250.79   3.303%   $259.0736   $259.07   $259.05   $259.10  
  Purchase #3 $185.93   9.664%   $203.8983   $203.90   $203.90   $203.90  
  Purchase #4 $6.70   4.468%   $6.9994   $7.00   $7.00   $7.00  
  Purchase #5 $228.36   3.651%   $236.6974   $236.70   $236.70   $236.70  
  Purchase #6 $102.86   12.184%   $115.3925   $115.39   $115.40   $115.40  
  Purchase #7 $24.70   3.482%   $25.5601   $25.56   $25.55   $25.60  
  7 purchase totals = $818.63       $868.5700   $868.57   $868.55   $868.60