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 $58.72   4.683%   $61.4699   $61.47   $61.45   $61.50  
  Purchase #2 $249.74   13.525%   $283.5173   $283.52   $283.50   $283.50  
  Purchase #3 $27.54   9.163%   $30.0635   $30.06   $30.05   $30.10  
  Purchase #4 $44.84   3.482%   $46.4013   $46.40   $46.40   $46.40  
  Purchase #5 $240.34   11.373%   $267.6739   $267.67   $267.65   $267.70  
  Purchase #6 $189.32   4.215%   $197.2998   $197.30   $197.30   $197.30  
  Purchase #7 $95.51   5.598%   $100.8566   $100.86   $100.85   $100.90  
  7 purchase totals = $906.01       $987.2823   $987.28   $987.20   $987.40