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	$75.59	10.340%	$83.406	$83.41	$83.40	$83.40
Purchase #2	$12.53	5.519%	$13.2215	$13.22	$13.20	$13.20
Purchase #3	$121.57	8.400%	$131.7819	$131.78	$131.80	$131.80
Purchase #4	$237.42	3.424%	$245.5493	$245.55	$245.55	$245.50
Purchase #5	$13.51	5.862%	$14.302	$14.30	$14.30	$14.30
Purchase #6	$79.32	13.159%	$89.7577	$89.76	$89.75	$89.80
Purchase #7	$93.86	8.298%	$101.6485	$101.65	$101.65	$101.60
7 purchase totals =	$633.80		$679.6669	$679.67	$679.65	$679.60