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	$154.66	4.319%	$161.3398	$161.34	$161.35	$161.30
Purchase #2	$173.57	5.538%	$183.1823	$183.18	$183.20	$183.20
Purchase #3	$132.55	5.305%	$139.5818	$139.58	$139.60	$139.60
Purchase #4	$59.60	3.475%	$61.6711	$61.67	$61.65	$61.70
Purchase #5	$177.35	12.138%	$198.8767	$198.88	$198.90	$198.90
Purchase #6	$139.46	12.519%	$156.919	$156.92	$156.90	$156.90
Purchase #7	$150.35	9.753%	$165.0136	$165.01	$165.00	$165.00
7 purchase totals =	$987.54		$1,066.5843	$1,066.58	$1,066.60	$1,066.60