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 $210.59   6.162%   $223.5666   $223.57   $223.55   $223.60  
  Purchase #2 $249.71   6.229%   $265.2644   $265.26   $265.25   $265.30  
  Purchase #3 $6.75   8.427%   $7.3188   $7.32   $7.30   $7.30  
  Purchase #4 $145.93   13.683%   $165.8976   $165.90   $165.90   $165.90  
  Purchase #5 $46.99   9.275%   $51.3483   $51.35   $51.35   $51.30  
  Purchase #6 $161.75   10.383%   $178.5445   $178.54   $178.55   $178.50  
  Purchase #7 $241.50   12.596%   $271.9193   $271.92   $271.90   $271.90  
  7 purchase totals = $1,063.22       $1,163.8595   $1,163.86   $1,163.80   $1,163.80