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	$196.51	12.663%	$221.3941	$221.39	$221.40	$221.40
Purchase #2	$61.41	11.487%	$68.4642	$68.46	$68.45	$68.50
Purchase #3	$29.74	13.730%	$33.8233	$33.82	$33.80	$33.80
Purchase #4	$37.38	10.377%	$41.2589	$41.26	$41.25	$41.30
Purchase #5	$222.75	7.355%	$239.1333	$239.13	$239.15	$239.10
Purchase #6	$120.36	9.583%	$131.8941	$131.89	$131.90	$131.90
Purchase #7	$50.75	8.201%	$54.912	$54.91	$54.90	$54.90
7 purchase totals =	$718.90		$790.8799	$790.86	$790.85	$790.90