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 $249.67   10.383%   $275.5932   $275.59   $275.60   $275.60  
  Purchase #2 $24.98   6.499%   $26.6035   $26.60   $26.60   $26.60  
  Purchase #3 $7.75   10.321%   $8.5499   $8.55   $8.55   $8.50  
  Purchase #4 $246.79   4.415%   $257.6858   $257.69   $257.70   $257.70  
  Purchase #5 $179.32   3.873%   $186.2651   $186.27   $186.25   $186.30  
  Purchase #6 $144.87   12.419%   $162.8614   $162.86   $162.85   $162.90  
  Purchase #7 $167.70   7.733%   $180.6682   $180.67   $180.65   $180.70  
  7 purchase totals = $1,021.08       $1,098.2271   $1,098.23   $1,098.20   $1,098.30