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	$135.42	12.814%	$152.7727	$152.77	$152.75	$152.80
Purchase #2	$42.65	7.173%	$45.7093	$45.71	$45.70	$45.70
Purchase #3	$137.91	8.512%	$149.6489	$149.65	$149.65	$149.60
Purchase #4	$216.75	7.739%	$233.5243	$233.52	$233.50	$233.50
Purchase #5	$83.92	6.750%	$89.5846	$89.58	$89.60	$89.60
Purchase #6	$140.52	3.357%	$145.2373	$145.24	$145.25	$145.20
Purchase #7	$188.33	13.184%	$213.1594	$213.16	$213.15	$213.20
7 purchase totals =	$945.50		$1,029.6365	$1,029.63	$1,029.60	$1,029.60