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	$89.76	11.809%	$100.3598	$100.36	$100.35	$100.40
Purchase #2	$113.91	4.198%	$118.6919	$118.69	$118.70	$118.70
Purchase #3	$124.57	13.146%	$140.946	$140.95	$140.95	$140.90
Purchase #4	$50.97	13.245%	$57.721	$57.72	$57.70	$57.70
Purchase #5	$217.76	5.273%	$229.2425	$229.24	$229.25	$229.20
Purchase #6	$218.30	12.385%	$245.3365	$245.34	$245.35	$245.30
Purchase #7	$73.97	5.629%	$78.1338	$78.13	$78.15	$78.10
7 purchase totals =	$889.24		$970.4315	$970.43	$970.45	$970.30