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	$86.54	3.291%	$89.388	$89.39	$89.40	$89.40
Purchase #2	$133.81	5.414%	$141.0545	$141.05	$141.05	$141.10
Purchase #3	$38.87	12.411%	$43.6942	$43.69	$43.70	$43.70
Purchase #4	$135.35	3.762%	$140.4419	$140.44	$140.45	$140.40
Purchase #5	$80.26	12.384%	$90.1994	$90.20	$90.20	$90.20
Purchase #6	$195.70	13.768%	$222.644	$222.64	$222.65	$222.60
Purchase #7	$149.74	11.825%	$167.4468	$167.45	$167.45	$167.40
7 purchase totals =	$820.27		$894.8688	$894.86	$894.90	$894.80