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 $74.99   10.197%   $82.6367   $82.64   $82.65   $82.60  
  Purchase #2 $241.36   9.316%   $263.8451   $263.85   $263.85   $263.80  
  Purchase #3 $155.67   3.827%   $161.6275   $161.63   $161.65   $161.60  
  Purchase #4 $244.66   5.690%   $258.5812   $258.58   $258.60   $258.60  
  Purchase #5 $161.41   8.771%   $175.5673   $175.57   $175.55   $175.60  
  Purchase #6 $233.38   8.558%   $253.3527   $253.35   $253.35   $253.40  
  Purchase #7 $20.80   5.461%   $21.9359   $21.94   $21.95   $21.90  
  7 purchase totals = $1,132.27       $1,217.5464   $1,217.56   $1,217.60   $1,217.50