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 $14.54   8.488%   $15.7742   $15.77   $15.75   $15.80  
  Purchase #2 $132.59   11.321%   $147.6005   $147.60   $147.60   $147.60  
  Purchase #3 $78.30   7.192%   $83.9313   $83.93   $83.95   $83.90  
  Purchase #4 $237.91   6.619%   $253.6573   $253.66   $253.65   $253.70  
  Purchase #5 $76.32   10.412%   $84.2664   $84.27   $84.25   $84.30  
  Purchase #6 $136.25   3.821%   $141.4561   $141.46   $141.45   $141.50  
  Purchase #7 $211.30   3.677%   $219.0695   $219.07   $219.05   $219.10  
  7 purchase totals = $887.21       $945.7553   $945.76   $945.70   $945.90