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	$51.27	10.615%	$56.7123	$56.71	$56.70	$56.70
Purchase #2	$242.59	3.196%	$250.3432	$250.34	$250.35	$250.30
Purchase #3	$115.54	3.622%	$119.7249	$119.72	$119.70	$119.70
Purchase #4	$49.32	8.266%	$53.3968	$53.40	$53.40	$53.40
Purchase #5	$187.88	4.842%	$196.9771	$196.98	$197.00	$197.00
Purchase #6	$233.39	12.160%	$261.7702	$261.77	$261.75	$261.80
Purchase #7	$6.78	9.488%	$7.4233	$7.42	$7.40	$7.40
7 purchase totals =	$886.77		$946.3478	$946.34	$946.30	$946.30