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	$56.39	7.393%	$60.5589	$60.56	$60.55	$60.60
Purchase #2	$32.87	9.215%	$35.899	$35.90	$35.90	$35.90
Purchase #3	$122.71	7.182%	$131.523	$131.52	$131.50	$131.50
Purchase #4	$191.63	11.212%	$213.1156	$213.12	$213.10	$213.10
Purchase #5	$138.41	5.804%	$146.4433	$146.44	$146.45	$146.40
Purchase #6	$58.98	9.565%	$64.6214	$64.62	$64.60	$64.60
Purchase #7	$156.90	11.776%	$175.3765	$175.38	$175.40	$175.40
7 purchase totals =	$757.89		$827.5377	$827.54	$827.50	$827.50