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	$169.43	5.363%	$178.5165	$178.52	$178.50	$178.50
Purchase #2	$200.57	7.711%	$216.036	$216.04	$216.05	$216.00
Purchase #3	$85.85	7.497%	$92.2862	$92.29	$92.30	$92.30
Purchase #4	$87.38	5.788%	$92.4376	$92.44	$92.45	$92.40
Purchase #5	$155.44	7.136%	$166.5322	$166.53	$166.55	$166.50
Purchase #6	$116.51	12.802%	$131.4256	$131.43	$131.45	$131.40
Purchase #7	$9.87	13.643%	$11.2166	$11.22	$11.20	$11.20
7 purchase totals =	$825.05		$888.4507	$888.47	$888.50	$888.30