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	$89.27	5.664%	$94.3263	$94.33	$94.35	$94.30
Purchase #2	$106.69	5.198%	$112.2357	$112.24	$112.25	$112.20
Purchase #3	$233.84	7.520%	$251.4248	$251.42	$251.40	$251.40
Purchase #4	$76.59	11.253%	$85.2087	$85.21	$85.20	$85.20
Purchase #5	$97.53	3.505%	$100.9484	$100.95	$100.95	$100.90
Purchase #6	$88.46	7.827%	$95.3838	$95.38	$95.40	$95.40
Purchase #7	$100.95	10.635%	$111.686	$111.69	$111.70	$111.70
7 purchase totals =	$793.33		$851.2137	$851.22	$851.25	$851.10