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	$134.99	12.502%	$151.8664	$151.87	$151.85	$151.90
Purchase #2	$28.57	13.661%	$32.4729	$32.47	$32.45	$32.50
Purchase #3	$21.72	12.791%	$24.4982	$24.50	$24.50	$24.50
Purchase #4	$237.93	5.267%	$250.4618	$250.46	$250.45	$250.50
Purchase #5	$155.42	12.707%	$175.1692	$175.17	$175.15	$175.20
Purchase #6	$172.76	7.705%	$186.0712	$186.07	$186.05	$186.10
Purchase #7	$218.58	8.561%	$237.2926	$237.29	$237.30	$237.30
7 purchase totals =	$969.97		$1,057.8323	$1,057.83	$1,057.75	$1,058.00