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 $90.48   8.387%   $98.0686   $98.07   $98.05   $98.10  
  Purchase #2 $197.97   10.439%   $218.6361   $218.64   $218.65   $218.60  
  Purchase #3 $24.88   4.253%   $25.9381   $25.94   $25.95   $25.90  
  Purchase #4 $221.67   5.776%   $234.4737   $234.47   $234.45   $234.50  
  Purchase #5 $204.49   13.673%   $232.4499   $232.45   $232.45   $232.40  
  Purchase #6 $195.90   4.379%   $204.4785   $204.48   $204.50   $204.50  
  Purchase #7 $27.37   7.682%   $29.4726   $29.47   $29.45   $29.50  
  7 purchase totals = $962.76       $1,043.5175   $1,043.52   $1,043.50   $1,043.50