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 $58.82   3.317%   $60.7711   $60.77   $60.75   $60.80  
  Purchase #2 $199.55   13.723%   $226.9342   $226.93   $226.95   $226.90  
  Purchase #3 $20.36   9.397%   $22.2732   $22.27   $22.25   $22.30  
  Purchase #4 $180.97   8.558%   $196.4574   $196.46   $196.45   $196.50  
  Purchase #5 $177.84   4.313%   $185.5102   $185.51   $185.50   $185.50  
  Purchase #6 $6.99   8.541%   $7.587   $7.59   $7.60   $7.60  
  Purchase #7 $24.43   13.655%   $27.7659   $27.77   $27.75   $27.80  
  7 purchase totals = $668.96       $727.2990   $727.30   $727.25   $727.40