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	$52.60	8.598%	$57.1225	$57.12	$57.10	$57.10
Purchase #2	$34.72	13.755%	$39.4957	$39.50	$39.50	$39.50
Purchase #3	$105.47	5.410%	$111.1759	$111.18	$111.20	$111.20
Purchase #4	$166.42	12.294%	$186.8797	$186.88	$186.90	$186.90
Purchase #5	$228.67	5.265%	$240.7095	$240.71	$240.70	$240.70
Purchase #6	$72.84	7.793%	$78.5164	$78.52	$78.50	$78.50
Purchase #7	$162.95	7.437%	$175.0686	$175.07	$175.05	$175.10
7 purchase totals =	$823.67		$888.9683	$888.98	$888.95	$889.00