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	$158.73	3.471%	$164.2395	$164.24	$164.25	$164.20
Purchase #2	$140.67	6.735%	$150.1441	$150.14	$150.15	$150.10
Purchase #3	$33.92	11.329%	$37.7628	$37.76	$37.75	$37.80
Purchase #4	$213.92	4.624%	$223.8117	$223.81	$223.80	$223.80
Purchase #5	$157.45	8.850%	$171.3843	$171.38	$171.40	$171.40
Purchase #6	$45.73	9.803%	$50.2129	$50.21	$50.20	$50.20
Purchase #7	$43.71	10.671%	$48.3743	$48.37	$48.35	$48.40
7 purchase totals =	$794.13		$845.9296	$845.91	$845.90	$845.90