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	$33.85	12.362%	$38.0345	$38.03	$38.05	$38.00
Purchase #2	$145.63	6.364%	$154.8979	$154.90	$154.90	$154.90
Purchase #3	$88.74	9.423%	$97.102	$97.10	$97.10	$97.10
Purchase #4	$72.51	10.762%	$80.3135	$80.31	$80.30	$80.30
Purchase #5	$23.69	3.718%	$24.5708	$24.57	$24.55	$24.60
Purchase #6	$106.57	4.608%	$111.4807	$111.48	$111.50	$111.50
Purchase #7	$53.25	3.560%	$55.1457	$55.15	$55.15	$55.10
7 purchase totals =	$524.24		$561.5451	$561.54	$561.55	$561.50