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	$139.75	4.714%	$146.3378	$146.34	$146.35	$146.30
Purchase #2	$51.71	3.352%	$53.4433	$53.44	$53.45	$53.40
Purchase #3	$101.40	10.123%	$111.6647	$111.66	$111.65	$111.70
Purchase #4	$86.54	7.302%	$92.8592	$92.86	$92.85	$92.90
Purchase #5	$195.26	12.819%	$220.2904	$220.29	$220.30	$220.30
Purchase #6	$203.75	6.628%	$217.2546	$217.25	$217.25	$217.30
Purchase #7	$70.72	11.272%	$78.6916	$78.69	$78.70	$78.70
7 purchase totals =	$849.13		$920.5416	$920.53	$920.55	$920.60