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	$86.34	6.736%	$92.1559	$92.16	$92.15	$92.20
Purchase #2	$59.36	9.210%	$64.8271	$64.83	$64.85	$64.80
Purchase #3	$158.68	8.563%	$172.2678	$172.27	$172.25	$172.30
Purchase #4	$213.43	4.153%	$222.2937	$222.29	$222.30	$222.30
Purchase #5	$113.90	11.773%	$127.3094	$127.31	$127.30	$127.30
Purchase #6	$213.43	5.708%	$225.6126	$225.61	$225.60	$225.60
Purchase #7	$30.49	13.417%	$34.5808	$34.58	$34.60	$34.60
7 purchase totals =	$875.63		$939.0473	$939.05	$939.05	$939.10