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	$223.88	6.640%	$238.7456	$238.75	$238.75	$238.70
Purchase #2	$59.26	13.228%	$67.0989	$67.10	$67.10	$67.10
Purchase #3	$111.89	10.549%	$123.6933	$123.69	$123.70	$123.70
Purchase #4	$150.90	5.760%	$159.5918	$159.59	$159.60	$159.60
Purchase #5	$78.66	12.750%	$88.6892	$88.69	$88.70	$88.70
Purchase #6	$37.54	6.695%	$40.0533	$40.05	$40.05	$40.10
Purchase #7	$190.51	12.603%	$214.52	$214.52	$214.50	$214.50
7 purchase totals =	$852.64		$932.3921	$932.39	$932.40	$932.40