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	$164.25	4.257%	$171.2421	$171.24	$171.25	$171.20
Purchase #2	$131.65	11.640%	$146.9741	$146.97	$146.95	$147.00
Purchase #3	$74.45	5.870%	$78.8202	$78.82	$78.80	$78.80
Purchase #4	$233.48	10.445%	$257.867	$257.87	$257.85	$257.90
Purchase #5	$118.57	11.104%	$131.736	$131.74	$131.75	$131.70
Purchase #6	$154.69	12.311%	$173.7339	$173.73	$173.75	$173.70
Purchase #7	$238.43	8.398%	$258.4534	$258.45	$258.45	$258.50
7 purchase totals =	$1,115.52		$1,218.8267	$1,218.82	$1,218.80	$1,218.80