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	$205.87	5.782%	$217.7734	$217.77	$217.75	$217.80
Purchase #2	$116.46	12.148%	$130.6076	$130.61	$130.60	$130.60
Purchase #3	$168.34	4.202%	$175.4136	$175.41	$175.40	$175.40
Purchase #4	$5.65	11.823%	$6.318	$6.32	$6.30	$6.30
Purchase #5	$37.79	13.658%	$42.9514	$42.95	$42.95	$43.00
Purchase #6	$153.94	7.684%	$165.7687	$165.77	$165.75	$165.80
Purchase #7	$152.81	12.655%	$172.1481	$172.15	$172.15	$172.10
7 purchase totals =	$840.86		$910.9808	$910.98	$910.90	$911.00