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 $132.53   11.864%   $148.2534   $148.25   $148.25   $148.30  
  Purchase #2 $43.33   8.247%   $46.9034   $46.90   $46.90   $46.90  
  Purchase #3 $143.53   7.815%   $154.7469   $154.75   $154.75   $154.70  
  Purchase #4 $24.92   5.294%   $26.2393   $26.24   $26.25   $26.20  
  Purchase #5 $239.44   11.474%   $266.9133   $266.91   $266.90   $266.90  
  Purchase #6 $16.99   5.556%   $17.934   $17.93   $17.95   $17.90  
  Purchase #7 $96.79   13.521%   $109.877   $109.88   $109.90   $109.90  
  7 purchase totals = $697.53       $770.8673   $770.86   $770.90   $770.80