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	$40.42	12.566%	$45.4992	$45.50	$45.50	$45.50
Purchase #2	$196.59	12.140%	$220.456	$220.46	$220.45	$220.50
Purchase #3	$136.44	5.270%	$143.6304	$143.63	$143.65	$143.60
Purchase #4	$36.42	11.361%	$40.5577	$40.56	$40.55	$40.60
Purchase #5	$204.91	7.181%	$219.6246	$219.62	$219.60	$219.60
Purchase #6	$173.31	4.114%	$180.44	$180.44	$180.45	$180.40
Purchase #7	$30.90	11.505%	$34.455	$34.46	$34.45	$34.50
7 purchase totals =	$818.99		$884.6629	$884.67	$884.65	$884.70