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	$42.63	8.821%	$46.3904	$46.39	$46.40	$46.40
Purchase #2	$169.93	10.740%	$188.1805	$188.18	$188.20	$188.20
Purchase #3	$187.89	4.178%	$195.74	$195.74	$195.75	$195.70
Purchase #4	$87.72	5.847%	$92.849	$92.85	$92.85	$92.80
Purchase #5	$84.50	7.527%	$90.8603	$90.86	$90.85	$90.90
Purchase #6	$93.42	11.173%	$103.8578	$103.86	$103.85	$103.90
Purchase #7	$64.99	11.122%	$72.2182	$72.22	$72.20	$72.20
7 purchase totals =	$731.08		$790.0962	$790.10	$790.10	$790.10