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	$18.86	8.842%	$20.5276	$20.53	$20.55	$20.50
Purchase #2	$65.36	11.358%	$72.7836	$72.78	$72.80	$72.80
Purchase #3	$101.89	10.748%	$112.8411	$112.84	$112.85	$112.80
Purchase #4	$77.89	5.231%	$81.9644	$81.96	$81.95	$82.00
Purchase #5	$150.72	11.710%	$168.3693	$168.37	$168.35	$168.40
Purchase #6	$240.91	5.423%	$253.9745	$253.97	$253.95	$254.00
Purchase #7	$181.57	5.601%	$191.7397	$191.74	$191.75	$191.70
7 purchase totals =	$837.20		$902.2002	$902.19	$902.20	$902.20