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 $47.52   4.664%   $49.7363   $49.74   $49.75   $49.70  
  Purchase #2 $24.42   10.604%   $27.0095   $27.01   $27.00   $27.00  
  Purchase #3 $60.46   4.692%   $63.2968   $63.30   $63.30   $63.30  
  Purchase #4 $56.46   12.523%   $63.5305   $63.53   $63.55   $63.50  
  Purchase #5 $231.71   9.405%   $253.5023   $253.50   $253.50   $253.50  
  Purchase #6 $50.56   11.477%   $56.3628   $56.36   $56.35   $56.40  
  Purchase #7 $232.97   7.835%   $251.2232   $251.22   $251.20   $251.20  
  7 purchase totals = $704.10       $764.6614   $764.66   $764.65   $764.60