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	$181.91	4.224%	$189.5939	$189.59	$189.60	$189.60
Purchase #2	$28.29	3.619%	$29.3138	$29.31	$29.30	$29.30
Purchase #3	$161.41	12.691%	$181.8945	$181.89	$181.90	$181.90
Purchase #4	$100.33	5.397%	$105.7448	$105.74	$105.75	$105.70
Purchase #5	$125.33	5.176%	$131.8171	$131.82	$131.80	$131.80
Purchase #6	$47.86	10.651%	$52.9576	$52.96	$52.95	$53.00
Purchase #7	$77.83	7.182%	$83.4198	$83.42	$83.40	$83.40
7 purchase totals =	$722.96		$774.7415	$774.73	$774.70	$774.70