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	$133.72	4.496%	$139.7321	$139.73	$139.75	$139.70
Purchase #2	$74.82	10.846%	$82.935	$82.94	$82.95	$82.90
Purchase #3	$131.69	5.637%	$139.1134	$139.11	$139.10	$139.10
Purchase #4	$50.47	10.593%	$55.8163	$55.82	$55.80	$55.80
Purchase #5	$165.95	4.361%	$173.1871	$173.19	$173.20	$173.20
Purchase #6	$149.60	6.297%	$159.0203	$159.02	$159.00	$159.00
Purchase #7	$175.86	5.800%	$186.0599	$186.06	$186.05	$186.10
7 purchase totals =	$882.11		$935.8641	$935.87	$935.85	$935.80