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 $247.38   3.392%   $255.7711   $255.77   $255.75   $255.80  
  Purchase #2 $26.95   10.250%   $29.7124   $29.71   $29.70   $29.70  
  Purchase #3 $68.51   12.252%   $76.9038   $76.90   $76.90   $76.90  
  Purchase #4 $121.71   3.419%   $125.8713   $125.87   $125.85   $125.90  
  Purchase #5 $131.92   11.499%   $147.0895   $147.09   $147.10   $147.10  
  Purchase #6 $194.95   11.309%   $216.9969   $217.00   $217.00   $217.00  
  Purchase #7 $165.33   5.143%   $173.8329   $173.83   $173.85   $173.80  
  7 purchase totals = $956.75       $1,026.1779   $1,026.17   $1,026.15   $1,026.20