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	$230.58	8.734%	$250.7189	$250.72	$250.70	$250.70
Purchase #2	$161.27	4.476%	$168.4884	$168.49	$168.50	$168.50
Purchase #3	$70.91	10.436%	$78.3102	$78.31	$78.30	$78.30
Purchase #4	$173.78	6.686%	$185.3989	$185.40	$185.40	$185.40
Purchase #5	$72.68	12.587%	$81.8282	$81.83	$81.85	$81.80
Purchase #6	$49.80	5.801%	$52.6889	$52.69	$52.70	$52.70
Purchase #7	$31.25	3.553%	$32.3603	$32.36	$32.35	$32.40
7 purchase totals =	$790.27		$849.7938	$849.80	$849.80	$849.80