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	$240.89	4.570%	$251.8987	$251.90	$251.90	$251.90
Purchase #2	$156.40	3.809%	$162.3573	$162.36	$162.35	$162.40
Purchase #3	$166.50	7.835%	$179.5453	$179.55	$179.55	$179.50
Purchase #4	$120.78	5.270%	$127.1451	$127.15	$127.15	$127.10
Purchase #5	$153.70	13.243%	$174.0545	$174.05	$174.05	$174.10
Purchase #6	$96.84	13.195%	$109.618	$109.62	$109.60	$109.60
Purchase #7	$172.72	9.766%	$189.5878	$189.59	$189.60	$189.60
7 purchase totals =	$1,107.83		$1,194.2067	$1,194.22	$1,194.20	$1,194.20