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	$94.43	8.699%	$102.6445	$102.64	$102.65	$102.60
Purchase #2	$216.83	3.694%	$224.8397	$224.84	$224.85	$224.80
Purchase #3	$57.79	5.398%	$60.9095	$60.91	$60.90	$60.90
Purchase #4	$85.49	4.684%	$89.4944	$89.49	$89.50	$89.50
Purchase #5	$176.61	12.823%	$199.2567	$199.26	$199.25	$199.30
Purchase #6	$105.28	8.107%	$113.815	$113.82	$113.80	$113.80
Purchase #7	$90.70	9.549%	$99.3609	$99.36	$99.35	$99.40
7 purchase totals =	$827.13		$890.3207	$890.32	$890.30	$890.30