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	$152.59	5.718%	$161.3151	$161.32	$161.30	$161.30
Purchase #2	$216.66	12.585%	$243.9267	$243.93	$243.95	$243.90
Purchase #3	$138.53	12.666%	$156.0762	$156.08	$156.10	$156.10
Purchase #4	$136.53	5.268%	$143.7224	$143.72	$143.70	$143.70
Purchase #5	$43.41	5.364%	$45.7385	$45.74	$45.75	$45.70
Purchase #6	$245.93	7.538%	$264.4682	$264.47	$264.45	$264.50
Purchase #7	$60.47	8.721%	$65.7436	$65.74	$65.75	$65.70
7 purchase totals =	$994.12		$1,080.9907	$1,081.00	$1,081.00	$1,080.90