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	$131.25	6.572%	$139.8758	$139.88	$139.90	$139.90
Purchase #2	$42.63	6.447%	$45.3784	$45.38	$45.40	$45.40
Purchase #3	$211.67	5.395%	$223.0896	$223.09	$223.10	$223.10
Purchase #4	$107.37	12.510%	$120.802	$120.80	$120.80	$120.80
Purchase #5	$145.54	7.187%	$156	$156.00	$156.00	$156.00
Purchase #6	$195.92	4.670%	$205.0695	$205.07	$205.05	$205.10
Purchase #7	$226.98	6.231%	$241.1231	$241.12	$241.10	$241.10
7 purchase totals =	$1,061.36		$1,131.3384	$1,131.34	$1,131.35	$1,131.40