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 $55.27   8.484%   $59.9591   $59.96   $59.95   $60.00  
  Purchase #2 $217.96   9.817%   $239.3571   $239.36   $239.35   $239.40  
  Purchase #3 $24.42   12.193%   $27.3975   $27.40   $27.40   $27.40  
  Purchase #4 $176.90   7.602%   $190.3479   $190.35   $190.35   $190.30  
  Purchase #5 $157.70   8.856%   $171.6659   $171.67   $171.65   $171.70  
  Purchase #6 $63.68   3.112%   $65.6617   $65.66   $65.65   $65.70  
  Purchase #7 $48.37   4.690%   $50.6386   $50.64   $50.65   $50.60  
  7 purchase totals = $744.30       $805.0278   $805.04   $805.00   $805.10