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	$46.69	10.368%	$51.5308	$51.53	$51.55	$51.50
Purchase #2	$95.74	8.164%	$103.5562	$103.56	$103.55	$103.60
Purchase #3	$52.33	4.581%	$54.7272	$54.73	$54.75	$54.70
Purchase #4	$12.81	7.578%	$13.7807	$13.78	$13.80	$13.80
Purchase #5	$218.81	11.738%	$244.4939	$244.49	$244.50	$244.50
Purchase #6	$37.32	4.588%	$39.0322	$39.03	$39.05	$39.00
Purchase #7	$77.62	5.272%	$81.7121	$81.71	$81.70	$81.70
7 purchase totals =	$541.32		$588.8331	$588.83	$588.90	$588.80