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 $53.86   13.205%   $60.9722   $60.97   $60.95   $61.00  
  Purchase #2 $54.39   11.614%   $60.7069   $60.71   $60.70   $60.70  
  Purchase #3 $96.45   7.362%   $103.5506   $103.55   $103.55   $103.60  
  Purchase #4 $18.88   5.820%   $19.9788   $19.98   $20.00   $20.00  
  Purchase #5 $125.71   8.110%   $135.9051   $135.91   $135.90   $135.90  
  Purchase #6 $82.38   10.461%   $90.9978   $91.00   $91.00   $91.00  
  Purchase #7 $61.35   9.729%   $67.3187   $67.32   $67.30   $67.30  
  7 purchase totals = $493.02       $539.4301   $539.44   $539.40   $539.50