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 $208.66   11.252%   $232.1384   $232.14   $232.15   $232.10  
  Purchase #2 $20.48   3.480%   $21.1927   $21.19   $21.20   $21.20  
  Purchase #3 $138.56   13.328%   $157.0273   $157.03   $157.05   $157.00  
  Purchase #4 $125.70   7.708%   $135.389   $135.39   $135.40   $135.40  
  Purchase #5 $138.93   12.562%   $156.3824   $156.38   $156.40   $156.40  
  Purchase #6 $199.46   9.320%   $218.0497   $218.05   $218.05   $218.00  
  Purchase #7 $77.90   11.225%   $86.6443   $86.64   $86.65   $86.60  
  7 purchase totals = $909.69       $1,006.8238   $1,006.82   $1,006.90   $1,006.70