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	$136.95	6.464%	$145.8024	$145.80	$145.80	$145.80
Purchase #2	$119.42	6.445%	$127.1166	$127.12	$127.10	$127.10
Purchase #3	$247.85	13.707%	$281.8228	$281.82	$281.80	$281.80
Purchase #4	$87.30	6.416%	$92.9012	$92.90	$92.90	$92.90
Purchase #5	$77.90	9.756%	$85.4999	$85.50	$85.50	$85.50
Purchase #6	$95.36	4.817%	$99.9535	$99.95	$99.95	$100.00
Purchase #7	$240.78	11.477%	$268.4143	$268.41	$268.40	$268.40
7 purchase totals =	$1,005.56		$1,101.5107	$1,101.50	$1,101.45	$1,101.50