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	$92.53	13.598%	$105.1122	$105.11	$105.10	$105.10
Purchase #2	$37.46	13.146%	$42.3845	$42.38	$42.40	$42.40
Purchase #3	$77.62	11.122%	$86.2529	$86.25	$86.25	$86.30
Purchase #4	$27.72	9.753%	$30.4235	$30.42	$30.40	$30.40
Purchase #5	$173.26	3.778%	$179.8058	$179.81	$179.80	$179.80
Purchase #6	$157.57	11.269%	$175.3266	$175.33	$175.35	$175.30
Purchase #7	$41.88	9.714%	$45.9482	$45.95	$45.95	$45.90
7 purchase totals =	$608.04		$665.2537	$665.25	$665.25	$665.20