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 $234.39   8.173%   $253.5467   $253.55   $253.55   $253.50  
  Purchase #2 $84.55   12.183%   $94.8507   $94.85   $94.85   $94.90  
  Purchase #3 $37.50   13.346%   $42.5048   $42.50   $42.50   $42.50  
  Purchase #4 $74.98   12.661%   $84.4732   $84.47   $84.45   $84.50  
  Purchase #5 $42.83   5.541%   $45.2032   $45.20   $45.20   $45.20  
  Purchase #6 $165.42   11.156%   $183.8743   $183.87   $183.85   $183.90  
  Purchase #7 $19.96   5.155%   $20.9889   $20.99   $21.00   $21.00  
  7 purchase totals = $659.63       $725.4418   $725.43   $725.40   $725.50