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	$153.69	3.686%	$159.355	$159.36	$159.35	$159.40
Purchase #2	$75.59	3.243%	$78.0414	$78.04	$78.05	$78.00
Purchase #3	$38.31	9.610%	$41.9916	$41.99	$42.00	$42.00
Purchase #4	$165.26	12.300%	$185.587	$185.59	$185.60	$185.60
Purchase #5	$95.81	11.279%	$106.6164	$106.62	$106.60	$106.60
Purchase #6	$223.88	8.242%	$242.3322	$242.33	$242.35	$242.30
Purchase #7	$103.27	3.264%	$106.6407	$106.64	$106.65	$106.60
7 purchase totals =	$855.81		$920.5643	$920.57	$920.60	$920.50