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 $164.55   10.813%   $182.3428   $182.34   $182.35   $182.30  
  Purchase #2 $69.98   12.226%   $78.5358   $78.54   $78.55   $78.50  
  Purchase #3 $235.92   5.165%   $248.1053   $248.11   $248.10   $248.10  
  Purchase #4 $60.27   10.669%   $66.7002   $66.70   $66.70   $66.70  
  Purchase #5 $142.54   3.119%   $146.9858   $146.99   $147.00   $147.00  
  Purchase #6 $247.60   13.117%   $280.0777   $280.08   $280.10   $280.10  
  Purchase #7 $237.37   5.561%   $250.5701   $250.57   $250.55   $250.60  
  7 purchase totals = $1,158.23       $1,253.3177   $1,253.33   $1,253.35   $1,253.30