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	$189.80	7.583%	$204.1925	$204.19	$204.20	$204.20
Purchase #2	$128.50	13.509%	$145.8591	$145.86	$145.85	$145.90
Purchase #3	$248.86	11.115%	$276.5208	$276.52	$276.50	$276.50
Purchase #4	$159.48	12.327%	$179.1391	$179.14	$179.15	$179.10
Purchase #5	$168.33	11.275%	$187.3092	$187.31	$187.30	$187.30
Purchase #6	$39.95	8.453%	$43.327	$43.33	$43.35	$43.30
Purchase #7	$55.51	4.166%	$57.8225	$57.82	$57.80	$57.80
7 purchase totals =	$990.43		$1,094.1702	$1,094.17	$1,094.15	$1,094.10