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	$118.88	7.141%	$127.3692	$127.37	$127.35	$127.40
Purchase #2	$100.25	4.651%	$104.9126	$104.91	$104.90	$104.90
Purchase #3	$106.41	8.429%	$115.3793	$115.38	$115.40	$115.40
Purchase #4	$137.46	8.354%	$148.9434	$148.94	$148.95	$148.90
Purchase #5	$86.74	3.653%	$89.9086	$89.91	$89.90	$89.90
Purchase #6	$156.96	9.473%	$171.8288	$171.83	$171.85	$171.80
Purchase #7	$7.80	8.766%	$8.4837	$8.48	$8.50	$8.50
7 purchase totals =	$714.50		$766.8256	$766.82	$766.85	$766.80