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	$173.25	6.859%	$185.1332	$185.13	$185.15	$185.10
Purchase #2	$61.49	3.614%	$63.7122	$63.71	$63.70	$63.70
Purchase #3	$52.69	5.443%	$55.5579	$55.56	$55.55	$55.60
Purchase #4	$77.72	11.170%	$86.4013	$86.40	$86.40	$86.40
Purchase #5	$98.41	3.180%	$101.5394	$101.54	$101.55	$101.50
Purchase #6	$104.66	5.784%	$110.7135	$110.71	$110.70	$110.70
Purchase #7	$211.34	3.330%	$218.3776	$218.38	$218.40	$218.40
7 purchase totals =	$779.56		$821.4351	$821.43	$821.45	$821.40