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	$142.63	3.218%	$147.2198	$147.22	$147.20	$147.20
Purchase #2	$79.86	7.843%	$86.1234	$86.12	$86.10	$86.10
Purchase #3	$174.45	6.128%	$185.1403	$185.14	$185.15	$185.10
Purchase #4	$135.39	13.606%	$153.8112	$153.81	$153.80	$153.80
Purchase #5	$80.31	11.170%	$89.2806	$89.28	$89.30	$89.30
Purchase #6	$225.42	8.291%	$244.1096	$244.11	$244.10	$244.10
Purchase #7	$153.73	3.853%	$159.6532	$159.65	$159.65	$159.70
7 purchase totals =	$991.79		$1,065.3381	$1,065.33	$1,065.30	$1,065.30