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 $90.62   8.703%   $98.5067   $98.51   $98.50   $98.50  
  Purchase #2 $114.75   4.473%   $119.8828   $119.88   $119.90   $119.90  
  Purchase #3 $118.99   5.470%   $125.4988   $125.50   $125.50   $125.50  
  Purchase #4 $104.48   9.713%   $114.6281   $114.63   $114.65   $114.60  
  Purchase #5 $14.93   9.239%   $16.3094   $16.31   $16.30   $16.30  
  Purchase #6 $111.52   9.625%   $122.2538   $122.25   $122.25   $122.30  
  Purchase #7 $221.95   5.313%   $233.7422   $233.74   $233.75   $233.70  
  7 purchase totals = $777.24       $830.8218   $830.82   $830.85   $830.80