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	$234.33	11.482%	$261.2358	$261.24	$261.25	$261.20
Purchase #2	$106.62	7.230%	$114.3286	$114.33	$114.35	$114.30
Purchase #3	$22.72	11.221%	$25.2694	$25.27	$25.25	$25.30
Purchase #4	$164.39	4.437%	$171.684	$171.68	$171.70	$171.70
Purchase #5	$247.32	6.245%	$262.7651	$262.77	$262.75	$262.80
Purchase #6	$27.73	3.856%	$28.7993	$28.80	$28.80	$28.80
Purchase #7	$99.52	11.695%	$111.1589	$111.16	$111.15	$111.20
7 purchase totals =	$902.63		$975.2411	$975.25	$975.25	$975.30