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	$196.53	13.407%	$222.8788	$222.88	$222.90	$222.90
Purchase #2	$235.75	6.178%	$250.3146	$250.31	$250.30	$250.30
Purchase #3	$250.32	9.388%	$273.82	$273.82	$273.80	$273.80
Purchase #4	$201.83	3.757%	$209.4128	$209.41	$209.40	$209.40
Purchase #5	$232.29	8.630%	$252.3366	$252.34	$252.35	$252.30
Purchase #6	$233.95	7.242%	$250.8927	$250.89	$250.90	$250.90
Purchase #7	$185.60	9.520%	$203.2691	$203.27	$203.25	$203.30
7 purchase totals =	$1,536.27		$1,662.9246	$1,662.92	$1,662.90	$1,662.90