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	$87.92	3.544%	$91.0359	$91.04	$91.05	$91.00
Purchase #2	$42.78	9.357%	$46.7829	$46.78	$46.80	$46.80
Purchase #3	$141.98	3.216%	$146.5461	$146.55	$146.55	$146.50
Purchase #4	$131.60	12.574%	$148.1474	$148.15	$148.15	$148.10
Purchase #5	$92.74	13.499%	$105.259	$105.26	$105.25	$105.30
Purchase #6	$131.76	13.855%	$150.0153	$150.02	$150.00	$150.00
Purchase #7	$159.45	12.839%	$179.9218	$179.92	$179.90	$179.90
7 purchase totals =	$788.23		$867.7084	$867.72	$867.70	$867.60