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	$40.64	5.626%	$42.9264	$42.93	$42.95	$42.90
Purchase #2	$153.88	12.608%	$173.2812	$173.28	$173.30	$173.30
Purchase #3	$80.49	11.514%	$89.7576	$89.76	$89.75	$89.80
Purchase #4	$99.54	11.825%	$111.3106	$111.31	$111.30	$111.30
Purchase #5	$161.98	4.306%	$168.9549	$168.95	$168.95	$169.00
Purchase #6	$194.97	3.471%	$201.7374	$201.74	$201.75	$201.70
Purchase #7	$50.29	13.408%	$57.0329	$57.03	$57.05	$57.00
7 purchase totals =	$781.79		$845.0010	$845.00	$845.05	$845.00