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	$131.78	4.401%	$137.5796	$137.58	$137.60	$137.60
Purchase #2	$201.44	10.467%	$222.5247	$222.52	$222.50	$222.50
Purchase #3	$102.51	3.190%	$105.7801	$105.78	$105.80	$105.80
Purchase #4	$211.69	3.435%	$218.9616	$218.96	$218.95	$219.00
Purchase #5	$99.31	4.451%	$103.7303	$103.73	$103.75	$103.70
Purchase #6	$225.34	13.703%	$256.2183	$256.22	$256.20	$256.20
Purchase #7	$118.51	7.744%	$127.6874	$127.69	$127.70	$127.70
7 purchase totals =	$1,090.58		$1,172.4820	$1,172.48	$1,172.50	$1,172.50