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	$73.48	9.639%	$80.5627	$80.56	$80.55	$80.60
Purchase #2	$94.66	8.698%	$102.8935	$102.89	$102.90	$102.90
Purchase #3	$138.58	12.621%	$156.0702	$156.07	$156.05	$156.10
Purchase #4	$13.79	12.443%	$15.5059	$15.51	$15.50	$15.50
Purchase #5	$65.38	9.604%	$71.6591	$71.66	$71.65	$71.70
Purchase #6	$138.79	9.673%	$152.2152	$152.22	$152.20	$152.20
Purchase #7	$141.58	8.337%	$153.3835	$153.38	$153.40	$153.40
7 purchase totals =	$666.26		$732.2901	$732.29	$732.25	$732.40