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	$52.64	12.335%	$59.1331	$59.13	$59.15	$59.10
Purchase #2	$118.91	13.542%	$135.0128	$135.01	$135.00	$135.00
Purchase #3	$93.81	12.316%	$105.3636	$105.36	$105.35	$105.40
Purchase #4	$59.73	12.431%	$67.155	$67.16	$67.15	$67.20
Purchase #5	$227.55	12.776%	$256.6218	$256.62	$256.60	$256.60
Purchase #6	$97.39	13.696%	$110.7285	$110.73	$110.75	$110.70
Purchase #7	$46.38	8.436%	$50.2926	$50.29	$50.30	$50.30
7 purchase totals =	$696.41		$784.3074	$784.30	$784.30	$784.30