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	$33.49	11.621%	$37.3819	$37.38	$37.40	$37.40
Purchase #2	$36.46	6.743%	$38.9185	$38.92	$38.90	$38.90
Purchase #3	$104.62	6.417%	$111.3335	$111.33	$111.35	$111.30
Purchase #4	$74.74	5.422%	$78.7924	$78.79	$78.80	$78.80
Purchase #5	$131.63	6.403%	$140.0583	$140.06	$140.05	$140.10
Purchase #6	$162.97	12.419%	$183.2092	$183.21	$183.20	$183.20
Purchase #7	$64.25	4.284%	$67.0025	$67.00	$67.00	$67.00
7 purchase totals =	$608.16		$656.6963	$656.69	$656.70	$656.70