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	$154.52	11.315%	$172.0039	$172.00	$172.00	$172.00
Purchase #2	$129.87	10.805%	$143.9025	$143.90	$143.90	$143.90
Purchase #3	$59.67	8.528%	$64.7587	$64.76	$64.75	$64.80
Purchase #4	$227.90	7.651%	$245.3366	$245.34	$245.35	$245.30
Purchase #5	$78.41	12.804%	$88.4496	$88.45	$88.45	$88.40
Purchase #6	$98.67	10.619%	$109.1478	$109.15	$109.15	$109.10
Purchase #7	$41.66	9.580%	$45.651	$45.65	$45.65	$45.70
7 purchase totals =	$790.70		$869.2501	$869.25	$869.25	$869.20