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	$92.52	11.714%	$103.3578	$103.36	$103.35	$103.40
Purchase #2	$72.65	3.763%	$75.3838	$75.38	$75.40	$75.40
Purchase #3	$174.47	11.225%	$194.0543	$194.05	$194.05	$194.10
Purchase #4	$48.61	13.708%	$55.2735	$55.27	$55.25	$55.30
Purchase #5	$60.31	11.388%	$67.1781	$67.18	$67.20	$67.20
Purchase #6	$160.90	12.479%	$180.9787	$180.98	$181.00	$181.00
Purchase #7	$57.86	7.663%	$62.2938	$62.29	$62.30	$62.30
7 purchase totals =	$667.32		$738.5200	$738.51	$738.55	$738.70