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	$227.42	8.711%	$247.2306	$247.23	$247.25	$247.20
Purchase #2	$139.70	9.113%	$152.4309	$152.43	$152.45	$152.40
Purchase #3	$25.82	8.351%	$27.9762	$27.98	$28.00	$28.00
Purchase #4	$49.82	6.734%	$53.1749	$53.17	$53.15	$53.20
Purchase #5	$32.35	4.162%	$33.6964	$33.70	$33.70	$33.70
Purchase #6	$36.44	11.545%	$40.647	$40.65	$40.65	$40.60
Purchase #7	$78.61	10.404%	$86.7886	$86.79	$86.80	$86.80
7 purchase totals =	$590.16		$641.9446	$641.95	$642.00	$641.90