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	$132.52	5.868%	$140.2963	$140.30	$140.30	$140.30
Purchase #2	$94.35	6.588%	$100.5658	$100.57	$100.55	$100.60
Purchase #3	$43.54	4.843%	$45.6486	$45.65	$45.65	$45.60
Purchase #4	$105.61	7.495%	$113.5255	$113.53	$113.55	$113.50
Purchase #5	$193.48	6.592%	$206.2342	$206.23	$206.25	$206.20
Purchase #6	$35.74	7.780%	$38.5206	$38.52	$38.50	$38.50
Purchase #7	$165.91	8.382%	$179.8166	$179.82	$179.80	$179.80
7 purchase totals =	$771.15		$824.6076	$824.62	$824.60	$824.50