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	$120.76	6.388%	$128.4741	$128.47	$128.45	$128.50
Purchase #2	$219.93	9.200%	$240.1636	$240.16	$240.15	$240.20
Purchase #3	$118.51	6.766%	$126.5284	$126.53	$126.55	$126.50
Purchase #4	$138.99	4.525%	$145.2793	$145.28	$145.30	$145.30
Purchase #5	$217.47	7.457%	$233.6867	$233.69	$233.70	$233.70
Purchase #6	$139.76	6.585%	$148.9632	$148.96	$148.95	$149.00
Purchase #7	$131.88	7.211%	$141.3899	$141.39	$141.40	$141.40
7 purchase totals =	$1,087.30		$1,164.4852	$1,164.48	$1,164.50	$1,164.60