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	$225.71	7.326%	$242.2455	$242.25	$242.25	$242.20
Purchase #2	$53.78	4.442%	$56.1689	$56.17	$56.15	$56.20
Purchase #3	$136.31	6.789%	$145.5641	$145.56	$145.55	$145.60
Purchase #4	$61.30	13.602%	$69.638	$69.64	$69.65	$69.60
Purchase #5	$223.98	13.732%	$254.7369	$254.74	$254.75	$254.70
Purchase #6	$96.30	9.741%	$105.6806	$105.68	$105.70	$105.70
Purchase #7	$39.40	11.400%	$43.8916	$43.89	$43.90	$43.90
7 purchase totals =	$836.78		$917.9256	$917.93	$917.95	$917.90