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	$83.70	10.538%	$92.5203	$92.52	$92.50	$92.50
Purchase #2	$131.98	5.368%	$139.0647	$139.06	$139.05	$139.10
Purchase #3	$52.92	11.736%	$59.1307	$59.13	$59.15	$59.10
Purchase #4	$201.68	9.793%	$221.4305	$221.43	$221.45	$221.40
Purchase #5	$77.50	3.576%	$80.2714	$80.27	$80.25	$80.30
Purchase #6	$157.87	8.699%	$171.6031	$171.60	$171.60	$171.60
Purchase #7	$113.73	10.648%	$125.84	$125.84	$125.85	$125.80
7 purchase totals =	$819.38		$889.8607	$889.85	$889.85	$889.80