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	$179.37	5.336%	$188.9412	$188.94	$188.95	$188.90
Purchase #2	$30.37	8.195%	$32.8588	$32.86	$32.85	$32.90
Purchase #3	$41.26	10.664%	$45.66	$45.66	$45.65	$45.70
Purchase #4	$28.63	3.225%	$29.5533	$29.55	$29.55	$29.60
Purchase #5	$146.35	13.102%	$165.5248	$165.52	$165.50	$165.50
Purchase #6	$182.90	9.711%	$200.6614	$200.66	$200.65	$200.70
Purchase #7	$136.26	10.169%	$150.1163	$150.12	$150.10	$150.10
7 purchase totals =	$745.14		$813.3158	$813.31	$813.25	$813.40