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 $24.34   8.551%   $26.4213   $26.42   $26.40   $26.40  
  Purchase #2 $119.98   4.623%   $125.5267   $125.53   $125.55   $125.50  
  Purchase #3 $142.53   9.610%   $156.2271   $156.23   $156.25   $156.20  
  Purchase #4 $172.46   8.549%   $187.2036   $187.20   $187.20   $187.20  
  Purchase #5 $93.33   12.257%   $104.7695   $104.77   $104.75   $104.80  
  Purchase #6 $175.81   5.715%   $185.8575   $185.86   $185.85   $185.90  
  Purchase #7 $229.90   4.611%   $240.5007   $240.50   $240.50   $240.50  
  7 purchase totals = $958.35       $1,026.5064   $1,026.51   $1,026.50   $1,026.50