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	$88.87	12.768%	$100.2169	$100.22	$100.20	$100.20
Purchase #2	$250.86	9.862%	$275.5998	$275.60	$275.60	$275.60
Purchase #3	$240.67	8.780%	$261.8008	$261.80	$261.80	$261.80
Purchase #4	$12.46	9.603%	$13.6565	$13.66	$13.65	$13.70
Purchase #5	$96.48	13.842%	$109.8348	$109.83	$109.85	$109.80
Purchase #6	$61.40	8.328%	$66.5134	$66.51	$66.50	$66.50
Purchase #7	$204.84	6.473%	$218.0993	$218.10	$218.10	$218.10
7 purchase totals =	$955.58		$1,045.7215	$1,045.72	$1,045.70	$1,045.70