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	$33.84	10.264%	$37.3133	$37.31	$37.30	$37.30
Purchase #2	$74.73	6.406%	$79.5172	$79.52	$79.50	$79.50
Purchase #3	$200.59	12.373%	$225.409	$225.41	$225.40	$225.40
Purchase #4	$70.39	5.444%	$74.222	$74.22	$74.20	$74.20
Purchase #5	$57.86	6.190%	$61.4415	$61.44	$61.45	$61.40
Purchase #6	$161.77	11.862%	$180.9592	$180.96	$180.95	$181.00
Purchase #7	$70.42	11.140%	$78.2648	$78.26	$78.25	$78.30
7 purchase totals =	$669.60		$737.1270	$737.12	$737.05	$737.10