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	$236.94	5.463%	$249.884	$249.88	$249.90	$249.90
Purchase #2	$135.81	8.683%	$147.6024	$147.60	$147.60	$147.60
Purchase #3	$118.26	11.139%	$131.433	$131.43	$131.45	$131.40
Purchase #4	$76.80	7.169%	$82.3058	$82.31	$82.30	$82.30
Purchase #5	$145.29	7.603%	$156.3364	$156.34	$156.35	$156.30
Purchase #6	$76.89	3.729%	$79.7572	$79.76	$79.75	$79.80
Purchase #7	$127.96	13.431%	$145.1463	$145.15	$145.15	$145.10
7 purchase totals =	$917.95		$992.4651	$992.47	$992.50	$992.40