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	$226.87	12.156%	$254.4483	$254.45	$254.45	$254.40
Purchase #2	$174.56	5.661%	$184.4418	$184.44	$184.45	$184.40
Purchase #3	$240.80	7.683%	$259.3007	$259.30	$259.30	$259.30
Purchase #4	$96.72	3.302%	$99.9137	$99.91	$99.90	$99.90
Purchase #5	$129.52	5.340%	$136.4364	$136.44	$136.45	$136.40
Purchase #6	$138.80	8.275%	$150.2857	$150.29	$150.30	$150.30
Purchase #7	$117.95	13.517%	$133.8933	$133.89	$133.90	$133.90
7 purchase totals =	$1,125.22		$1,218.7199	$1,218.72	$1,218.75	$1,218.60