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	$18.32	6.615%	$19.5319	$19.53	$19.55	$19.50
Purchase #2	$156.36	7.531%	$168.1355	$168.14	$168.15	$168.10
Purchase #3	$71.35	6.814%	$76.2118	$76.21	$76.20	$76.20
Purchase #4	$76.27	12.525%	$85.8228	$85.82	$85.80	$85.80
Purchase #5	$97.95	13.719%	$111.3878	$111.39	$111.40	$111.40
Purchase #6	$66.42	7.739%	$71.5602	$71.56	$71.55	$71.60
Purchase #7	$221.32	11.567%	$246.9201	$246.92	$246.90	$246.90
7 purchase totals =	$707.99		$779.5701	$779.57	$779.55	$779.50