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	$79.36	3.474%	$82.117	$82.12	$82.10	$82.10
Purchase #2	$166.85	12.644%	$187.9465	$187.95	$187.95	$187.90
Purchase #3	$81.26	11.111%	$90.2888	$90.29	$90.30	$90.30
Purchase #4	$119.72	6.267%	$127.2229	$127.22	$127.20	$127.20
Purchase #5	$177.47	12.560%	$199.7602	$199.76	$199.75	$199.80
Purchase #6	$34.91	9.309%	$38.1598	$38.16	$38.15	$38.20
Purchase #7	$147.25	11.635%	$164.3825	$164.38	$164.40	$164.40
7 purchase totals =	$806.82		$889.8777	$889.88	$889.85	$889.90