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	$48.32	4.479%	$50.4843	$50.48	$50.50	$50.50
Purchase #2	$213.49	6.478%	$227.3199	$227.32	$227.30	$227.30
Purchase #3	$10.27	8.543%	$11.1474	$11.15	$11.15	$11.10
Purchase #4	$38.72	10.673%	$42.8526	$42.85	$42.85	$42.90
Purchase #5	$45.74	5.173%	$48.1061	$48.11	$48.10	$48.10
Purchase #6	$46.63	9.181%	$50.9111	$50.91	$50.90	$50.90
Purchase #7	$193.83	12.257%	$217.5877	$217.59	$217.60	$217.60
7 purchase totals =	$597.00		$648.4091	$648.41	$648.40	$648.40