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	$55.84	13.466%	$63.3594	$63.36	$63.35	$63.40
Purchase #2	$58.91	4.587%	$61.6122	$61.61	$61.60	$61.60
Purchase #3	$60.34	12.153%	$67.6731	$67.67	$67.65	$67.70
Purchase #4	$37.37	9.350%	$40.8641	$40.86	$40.85	$40.90
Purchase #5	$90.30	4.747%	$94.5865	$94.59	$94.60	$94.60
Purchase #6	$17.57	7.365%	$18.864	$18.86	$18.85	$18.90
Purchase #7	$145.28	12.648%	$163.655	$163.66	$163.65	$163.70
7 purchase totals =	$465.61		$510.6143	$510.61	$510.55	$510.80