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 $62.86   6.189%   $66.7504   $66.75   $66.75   $66.80  
  Purchase #2 $225.80   4.672%   $236.3494   $236.35   $236.35   $236.30  
  Purchase #3 $137.52   12.247%   $154.3621   $154.36   $154.35   $154.40  
  Purchase #4 $126.95   12.367%   $142.6499   $142.65   $142.65   $142.60  
  Purchase #5 $24.87   7.242%   $26.6711   $26.67   $26.65   $26.70  
  Purchase #6 $142.29   9.183%   $155.3565   $155.36   $155.35   $155.40  
  Purchase #7 $9.37   11.236%   $10.4228   $10.42   $10.40   $10.40  
  7 purchase totals = $729.66       $792.5622   $792.56   $792.50   $792.60