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	$171.46	4.743%	$179.5923	$179.59	$179.60	$179.60
Purchase #2	$105.75	13.592%	$120.1235	$120.12	$120.10	$120.10
Purchase #3	$243.28	10.410%	$268.6054	$268.61	$268.60	$268.60
Purchase #4	$241.33	3.245%	$249.1612	$249.16	$249.15	$249.20
Purchase #5	$184.34	13.848%	$209.8674	$209.87	$209.85	$209.90
Purchase #6	$74.63	13.848%	$84.9648	$84.96	$84.95	$85.00
Purchase #7	$64.67	11.112%	$71.8561	$71.86	$71.85	$71.90
7 purchase totals =	$1,085.46		$1,184.1707	$1,184.17	$1,184.10	$1,184.30