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 $22.99   12.554%   $25.8762   $25.88   $25.90   $25.90  
  Purchase #2 $220.45   11.696%   $246.2338   $246.23   $246.25   $246.20  
  Purchase #3 $108.29   13.583%   $122.999   $123.00   $123.00   $123.00  
  Purchase #4 $61.33   10.616%   $67.8408   $67.84   $67.85   $67.80  
  Purchase #5 $156.66   3.606%   $162.3092   $162.31   $162.30   $162.30  
  Purchase #6 $231.62   8.365%   $250.995   $251.00   $251.00   $251.00  
  Purchase #7 $125.33   13.534%   $142.2922   $142.29   $142.30   $142.30  
  7 purchase totals = $926.67       $1,018.5462   $1,018.55   $1,018.60   $1,018.50