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 $98.97   12.788%   $111.6263   $111.63   $111.65   $111.60  
  Purchase #2 $21.38   10.191%   $23.5588   $23.56   $23.55   $23.60  
  Purchase #3 $223.87   5.488%   $236.156   $236.16   $236.15   $236.20  
  Purchase #4 $192.57   9.571%   $211.0009   $211.00   $211.00   $211.00  
  Purchase #5 $156.27   3.284%   $161.4019   $161.40   $161.40   $161.40  
  Purchase #6 $225.84   9.766%   $247.8955   $247.90   $247.90   $247.90  
  Purchase #7 $50.57   4.843%   $53.0191   $53.02   $53.00   $53.00  
  7 purchase totals = $969.47       $1,044.6585   $1,044.67   $1,044.65   $1,044.70