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	$63.55	5.728%	$67.1901	$67.19	$67.20	$67.20
Purchase #2	$249.42	11.415%	$277.8913	$277.89	$277.90	$277.90
Purchase #3	$16.73	11.153%	$18.5959	$18.60	$18.60	$18.60
Purchase #4	$130.39	4.389%	$136.1128	$136.11	$136.10	$136.10
Purchase #5	$179.91	7.553%	$193.4986	$193.50	$193.50	$193.50
Purchase #6	$161.59	11.414%	$180.0339	$180.03	$180.05	$180.00
Purchase #7	$181.92	3.425%	$188.1508	$188.15	$188.15	$188.20
7 purchase totals =	$983.51		$1,061.4734	$1,061.47	$1,061.50	$1,061.50