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	$58.74	13.774%	$66.8308	$66.83	$66.85	$66.80
Purchase #2	$231.88	12.657%	$261.2291	$261.23	$261.25	$261.20
Purchase #3	$100.56	6.319%	$106.9144	$106.91	$106.90	$106.90
Purchase #4	$67.74	7.313%	$72.6938	$72.69	$72.70	$72.70
Purchase #5	$87.61	3.674%	$90.8288	$90.83	$90.85	$90.80
Purchase #6	$117.36	7.632%	$126.3169	$126.32	$126.30	$126.30
Purchase #7	$101.81	4.229%	$106.1155	$106.12	$106.10	$106.10
7 purchase totals =	$765.70		$830.9293	$830.93	$830.95	$830.80