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	$93.78	5.480%	$98.9191	$98.92	$98.90	$98.90
Purchase #2	$66.34	7.311%	$71.1901	$71.19	$71.20	$71.20
Purchase #3	$178.93	4.236%	$186.5095	$186.51	$186.50	$186.50
Purchase #4	$57.70	13.853%	$65.6932	$65.69	$65.70	$65.70
Purchase #5	$53.41	13.267%	$60.4959	$60.50	$60.50	$60.50
Purchase #6	$146.42	4.839%	$153.5053	$153.51	$153.50	$153.50
Purchase #7	$202.80	13.205%	$229.5797	$229.58	$229.60	$229.60
7 purchase totals =	$799.38		$865.8928	$865.90	$865.90	$865.90