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	$206.86	11.741%	$231.1474	$231.15	$231.15	$231.10
Purchase #2	$213.44	11.145%	$237.2279	$237.23	$237.25	$237.20
Purchase #3	$193.55	6.849%	$206.8062	$206.81	$206.80	$206.80
Purchase #4	$103.73	12.329%	$116.5189	$116.52	$116.50	$116.50
Purchase #5	$109.85	10.399%	$121.2733	$121.27	$121.25	$121.30
Purchase #6	$73.61	12.472%	$82.7906	$82.79	$82.80	$82.80
Purchase #7	$243.52	6.172%	$258.5501	$258.55	$258.55	$258.60
7 purchase totals =	$1,144.56		$1,254.3144	$1,254.32	$1,254.30	$1,254.30