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	$209.28	9.304%	$228.7514	$228.75	$228.75	$228.80
Purchase #2	$56.40	5.360%	$59.423	$59.42	$59.40	$59.40
Purchase #3	$46.61	6.864%	$49.8093	$49.81	$49.80	$49.80
Purchase #4	$28.82	3.872%	$29.9359	$29.94	$29.95	$29.90
Purchase #5	$66.56	9.371%	$72.7973	$72.80	$72.80	$72.80
Purchase #6	$26.86	9.148%	$29.3172	$29.32	$29.30	$29.30
Purchase #7	$158.63	4.784%	$166.2189	$166.22	$166.20	$166.20
7 purchase totals =	$593.16		$636.2530	$636.26	$636.20	$636.20