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	$5.78	10.767%	$6.4023	$6.40	$6.40	$6.40
Purchase #2	$222.50	8.528%	$241.4748	$241.47	$241.45	$241.50
Purchase #3	$26.26	9.263%	$28.6925	$28.69	$28.70	$28.70
Purchase #4	$182.62	11.832%	$204.2276	$204.23	$204.25	$204.20
Purchase #5	$249.86	7.483%	$268.557	$268.56	$268.55	$268.60
Purchase #6	$231.84	10.818%	$256.9205	$256.92	$256.90	$256.90
Purchase #7	$92.66	11.759%	$103.5559	$103.56	$103.55	$103.60
7 purchase totals =	$1,011.52		$1,109.8306	$1,109.83	$1,109.80	$1,109.90