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	$94.46	5.187%	$99.3596	$99.36	$99.35	$99.40
Purchase #2	$222.66	11.575%	$248.4329	$248.43	$248.45	$248.40
Purchase #3	$137.30	4.780%	$143.8629	$143.86	$143.85	$143.90
Purchase #4	$75.88	9.123%	$82.8025	$82.80	$82.80	$82.80
Purchase #5	$102.31	6.477%	$108.9366	$108.94	$108.95	$108.90
Purchase #6	$86.88	9.562%	$95.1875	$95.19	$95.20	$95.20
Purchase #7	$133.46	11.326%	$148.5757	$148.58	$148.60	$148.60
7 purchase totals =	$852.95		$927.1577	$927.16	$927.20	$927.20