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	$73.50	6.377%	$78.1871	$78.19	$78.20	$78.20
Purchase #2	$41.31	9.454%	$45.2154	$45.22	$45.20	$45.20
Purchase #3	$141.60	9.836%	$155.5278	$155.53	$155.55	$155.50
Purchase #4	$222.50	12.458%	$250.2191	$250.22	$250.20	$250.20
Purchase #5	$115.42	6.821%	$123.2928	$123.29	$123.30	$123.30
Purchase #6	$108.95	10.776%	$120.6905	$120.69	$120.70	$120.70
Purchase #7	$62.34	13.745%	$70.9086	$70.91	$70.90	$70.90
7 purchase totals =	$765.62		$844.0413	$844.05	$844.05	$844.00