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 $23.92   10.781%   $26.4988   $26.50   $26.50   $26.50  
  Purchase #2 $67.96   4.526%   $71.0359   $71.04   $71.05   $71.00  
  Purchase #3 $181.97   13.551%   $206.6288   $206.63   $206.65   $206.60  
  Purchase #4 $249.68   3.408%   $258.1891   $258.19   $258.20   $258.20  
  Purchase #5 $182.90   8.386%   $198.238   $198.24   $198.25   $198.20  
  Purchase #6 $32.53   10.699%   $36.0104   $36.01   $36.00   $36.00  
  Purchase #7 $212.77   9.179%   $232.3002   $232.30   $232.30   $232.30  
  7 purchase totals = $951.73       $1,028.9012   $1,028.91   $1,028.95   $1,028.80