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	$92.93	9.519%	$101.776	$101.78	$101.80	$101.80
Purchase #2	$89.52	7.469%	$96.2062	$96.21	$96.20	$96.20
Purchase #3	$107.44	3.481%	$111.18	$111.18	$111.20	$111.20
Purchase #4	$140.61	5.121%	$147.8106	$147.81	$147.80	$147.80
Purchase #5	$7.88	4.244%	$8.2144	$8.21	$8.20	$8.20
Purchase #6	$64.70	12.604%	$72.8548	$72.85	$72.85	$72.90
Purchase #7	$50.52	6.779%	$53.9448	$53.94	$53.95	$53.90
7 purchase totals =	$553.60		$591.9868	$591.98	$592.00	$592.00