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	$102.73	13.327%	$116.4208	$116.42	$116.40	$116.40
Purchase #2	$41.66	5.228%	$43.838	$43.84	$43.85	$43.80
Purchase #3	$212.87	12.363%	$239.1871	$239.19	$239.20	$239.20
Purchase #4	$37.72	9.307%	$41.2306	$41.23	$41.25	$41.20
Purchase #5	$79.39	3.770%	$82.383	$82.38	$82.40	$82.40
Purchase #6	$33.91	10.505%	$37.4722	$37.47	$37.45	$37.50
Purchase #7	$91.30	8.354%	$98.9272	$98.93	$98.95	$98.90
7 purchase totals =	$599.58		$659.4589	$659.46	$659.50	$659.40