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	$187.99	10.755%	$208.2083	$208.21	$208.20	$208.20
Purchase #2	$235.82	9.711%	$258.7205	$258.72	$258.70	$258.70
Purchase #3	$247.69	11.439%	$276.0233	$276.02	$276.00	$276.00
Purchase #4	$85.88	7.259%	$92.114	$92.11	$92.10	$92.10
Purchase #5	$94.51	6.238%	$100.4055	$100.41	$100.40	$100.40
Purchase #6	$50.85	12.700%	$57.308	$57.31	$57.30	$57.30
Purchase #7	$136.38	11.263%	$151.7405	$151.74	$151.75	$151.70
7 purchase totals =	$1,039.12		$1,144.5201	$1,144.52	$1,144.45	$1,144.40