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	$150.36	4.114%	$156.5458	$156.55	$156.55	$156.50
Purchase #2	$163.52	13.312%	$185.2878	$185.29	$185.30	$185.30
Purchase #3	$235.70	8.117%	$254.8318	$254.83	$254.85	$254.80
Purchase #4	$228.30	13.400%	$258.8922	$258.89	$258.90	$258.90
Purchase #5	$172.35	4.669%	$180.397	$180.40	$180.40	$180.40
Purchase #6	$80.84	11.806%	$90.384	$90.38	$90.40	$90.40
Purchase #7	$19.29	3.802%	$20.0234	$20.02	$20.00	$20.00
7 purchase totals =	$1,050.36		$1,146.3620	$1,146.36	$1,146.40	$1,146.30