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	$186.87	12.534%	$210.2923	$210.29	$210.30	$210.30
Purchase #2	$218.57	13.531%	$248.1447	$248.14	$248.15	$248.10
Purchase #3	$113.85	8.566%	$123.6024	$123.60	$123.60	$123.60
Purchase #4	$26.78	7.588%	$28.8121	$28.81	$28.80	$28.80
Purchase #5	$131.89	11.409%	$146.9373	$146.94	$146.95	$146.90
Purchase #6	$136.36	6.708%	$145.507	$145.51	$145.50	$145.50
Purchase #7	$243.88	10.453%	$269.3728	$269.37	$269.35	$269.40
7 purchase totals =	$1,058.20		$1,172.6686	$1,172.66	$1,172.65	$1,172.60