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	$18.60	6.659%	$19.8386	$19.84	$19.85	$19.80
Purchase #2	$37.36	8.623%	$40.5816	$40.58	$40.60	$40.60
Purchase #3	$10.27	6.176%	$10.9043	$10.90	$10.90	$10.90
Purchase #4	$74.98	13.751%	$85.2905	$85.29	$85.30	$85.30
Purchase #5	$174.77	5.350%	$184.1202	$184.12	$184.10	$184.10
Purchase #6	$98.83	5.735%	$104.4979	$104.50	$104.50	$104.50
Purchase #7	$119.82	9.605%	$131.3287	$131.33	$131.35	$131.30
7 purchase totals =	$534.63		$576.5618	$576.56	$576.60	$576.50