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 $244.89   8.256%   $265.1081   $265.11   $265.10   $265.10  
  Purchase #2 $183.87   10.779%   $203.6893   $203.69   $203.70   $203.70  
  Purchase #3 $19.51   11.224%   $21.6998   $21.70   $21.70   $21.70  
  Purchase #4 $221.90   13.824%   $252.5755   $252.58   $252.60   $252.60  
  Purchase #5 $108.56   8.156%   $117.4142   $117.41   $117.40   $117.40  
  Purchase #6 $98.65   5.415%   $103.9919   $103.99   $104.00   $104.00  
  Purchase #7 $71.47   11.338%   $79.5733   $79.57   $79.55   $79.60  
  7 purchase totals = $948.85       $1,044.0521   $1,044.05   $1,044.05   $1,044.10