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	$207.64	6.191%	$220.495	$220.50	$220.50	$220.50
Purchase #2	$175.34	12.307%	$196.9191	$196.92	$196.90	$196.90
Purchase #3	$158.46	9.183%	$173.0114	$173.01	$173.00	$173.00
Purchase #4	$63.61	10.846%	$70.5091	$70.51	$70.50	$70.50
Purchase #5	$76.76	11.370%	$85.4876	$85.49	$85.50	$85.50
Purchase #6	$130.86	3.515%	$135.4597	$135.46	$135.45	$135.50
Purchase #7	$249.36	5.516%	$263.1147	$263.11	$263.10	$263.10
7 purchase totals =	$1,062.03		$1,144.9966	$1,145.00	$1,144.95	$1,145.00