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	$10.48	3.751%	$10.8731	$10.87	$10.85	$10.90
Purchase #2	$179.41	7.531%	$192.9214	$192.92	$192.90	$192.90
Purchase #3	$118.32	11.445%	$131.8617	$131.86	$131.85	$131.90
Purchase #4	$235.56	4.152%	$245.3405	$245.34	$245.35	$245.30
Purchase #5	$90.38	10.397%	$99.7768	$99.78	$99.80	$99.80
Purchase #6	$76.51	3.461%	$79.158	$79.16	$79.15	$79.20
Purchase #7	$37.79	6.184%	$40.1269	$40.13	$40.15	$40.10
7 purchase totals =	$748.45		$800.0584	$800.06	$800.05	$800.10