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	$50.52	5.652%	$53.3754	$53.38	$53.40	$53.40
Purchase #2	$68.70	8.353%	$74.4385	$74.44	$74.45	$74.40
Purchase #3	$84.59	7.430%	$90.875	$90.88	$90.90	$90.90
Purchase #4	$240.37	10.202%	$264.8925	$264.89	$264.90	$264.90
Purchase #5	$60.45	12.102%	$67.7657	$67.77	$67.75	$67.80
Purchase #6	$35.84	9.671%	$39.3061	$39.31	$39.30	$39.30
Purchase #7	$80.56	9.581%	$88.2785	$88.28	$88.30	$88.30
7 purchase totals =	$621.03		$678.9317	$678.95	$679.00	$679.00