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	$38.45	12.265%	$43.1659	$43.17	$43.15	$43.20
Purchase #2	$111.86	4.631%	$117.0402	$117.04	$117.05	$117.00
Purchase #3	$167.52	10.479%	$185.0744	$185.07	$185.05	$185.10
Purchase #4	$193.56	6.545%	$206.2285	$206.23	$206.25	$206.20
Purchase #5	$78.93	4.222%	$82.2624	$82.26	$82.25	$82.30
Purchase #6	$94.56	8.148%	$102.2647	$102.26	$102.25	$102.30
Purchase #7	$91.83	7.238%	$98.4767	$98.48	$98.50	$98.50
7 purchase totals =	$776.71		$834.5128	$834.51	$834.50	$834.60