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	$129.62	6.830%	$138.473	$138.47	$138.45	$138.50
Purchase #2	$57.41	11.249%	$63.8681	$63.87	$63.85	$63.90
Purchase #3	$131.85	12.340%	$148.1203	$148.12	$148.10	$148.10
Purchase #4	$149.39	10.749%	$165.4479	$165.45	$165.45	$165.40
Purchase #5	$76.25	3.388%	$78.8334	$78.83	$78.85	$78.80
Purchase #6	$82.76	11.749%	$92.4835	$92.48	$92.50	$92.50
Purchase #7	$182.47	3.699%	$189.2196	$189.22	$189.20	$189.20
7 purchase totals =	$809.75		$876.4458	$876.44	$876.40	$876.40