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	$137.37	10.486%	$151.7746	$151.77	$151.75	$151.80
Purchase #2	$46.81	7.755%	$50.4401	$50.44	$50.45	$50.40
Purchase #3	$33.52	12.197%	$37.6084	$37.61	$37.60	$37.60
Purchase #4	$34.29	12.515%	$38.5814	$38.58	$38.60	$38.60
Purchase #5	$65.90	4.666%	$68.9749	$68.97	$68.95	$69.00
Purchase #6	$225.88	6.404%	$240.3454	$240.35	$240.35	$240.30
Purchase #7	$225.46	10.193%	$248.4411	$248.44	$248.45	$248.40
7 purchase totals =	$769.23		$836.1659	$836.16	$836.15	$836.10