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	$64.29	12.635%	$72.413	$72.41	$72.40	$72.40
Purchase #2	$70.70	10.644%	$78.2253	$78.23	$78.25	$78.20
Purchase #3	$40.96	5.312%	$43.1358	$43.14	$43.15	$43.10
Purchase #4	$153.72	4.182%	$160.1486	$160.15	$160.15	$160.10
Purchase #5	$21.33	4.567%	$22.3041	$22.30	$22.30	$22.30
Purchase #6	$56.99	9.253%	$62.2633	$62.26	$62.25	$62.30
Purchase #7	$147.48	3.656%	$152.8719	$152.87	$152.85	$152.90
7 purchase totals =	$555.47		$591.3620	$591.36	$591.35	$591.30