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	$236.49	9.781%	$259.6211	$259.62	$259.60	$259.60
Purchase #2	$18.50	13.522%	$21.0016	$21.00	$21.00	$21.00
Purchase #3	$74.48	7.657%	$80.1829	$80.18	$80.20	$80.20
Purchase #4	$250.52	4.437%	$261.6356	$261.64	$261.65	$261.60
Purchase #5	$153.77	9.607%	$168.5427	$168.54	$168.55	$168.50
Purchase #6	$228.28	13.406%	$258.8832	$258.88	$258.90	$258.90
Purchase #7	$96.50	13.586%	$109.6105	$109.61	$109.60	$109.60
7 purchase totals =	$1,058.54		$1,159.4776	$1,159.47	$1,159.50	$1,159.40