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	$153.72	4.248%	$160.25	$160.25	$160.25	$160.30
Purchase #2	$155.93	10.117%	$171.7054	$171.71	$171.70	$171.70
Purchase #3	$213.94	3.719%	$221.8964	$221.90	$221.90	$221.90
Purchase #4	$144.87	13.454%	$164.3608	$164.36	$164.35	$164.40
Purchase #5	$48.45	3.673%	$50.2296	$50.23	$50.25	$50.20
Purchase #6	$7.58	13.740%	$8.6215	$8.62	$8.60	$8.60
Purchase #7	$40.31	13.435%	$45.7256	$45.73	$45.75	$45.70
7 purchase totals =	$764.80		$822.7893	$822.80	$822.80	$822.80