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	$150.29	12.251%	$168.702	$168.70	$168.70	$168.70
Purchase #2	$147.97	12.816%	$166.9338	$166.93	$166.95	$166.90
Purchase #3	$117.46	11.631%	$131.1218	$131.12	$131.10	$131.10
Purchase #4	$137.73	4.450%	$143.859	$143.86	$143.85	$143.90
Purchase #5	$79.25	3.786%	$82.2504	$82.25	$82.25	$82.30
Purchase #6	$54.37	13.555%	$61.7399	$61.74	$61.75	$61.70
Purchase #7	$76.87	3.465%	$79.5335	$79.53	$79.55	$79.50
7 purchase totals =	$763.94		$834.1404	$834.13	$834.15	$834.10