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	$81.79	9.294%	$89.3916	$89.39	$89.40	$89.40
Purchase #2	$136.76	7.459%	$146.9609	$146.96	$146.95	$147.00
Purchase #3	$146.41	6.252%	$155.5636	$155.56	$155.55	$155.60
Purchase #4	$143.68	3.107%	$148.1441	$148.14	$148.15	$148.10
Purchase #5	$195.44	6.741%	$208.6146	$208.61	$208.60	$208.60
Purchase #6	$214.94	8.685%	$233.6075	$233.61	$233.60	$233.60
Purchase #7	$113.93	13.287%	$129.0679	$129.07	$129.05	$129.10
7 purchase totals =	$1,032.95		$1,111.3502	$1,111.34	$1,111.30	$1,111.40