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	$75.55	11.485%	$84.2269	$84.23	$84.25	$84.20
Purchase #2	$64.93	10.854%	$71.9775	$71.98	$72.00	$72.00
Purchase #3	$85.88	6.496%	$91.4588	$91.46	$91.45	$91.50
Purchase #4	$54.40	12.261%	$61.07	$61.07	$61.05	$61.10
Purchase #5	$36.31	3.184%	$37.4661	$37.47	$37.45	$37.50
Purchase #6	$223.94	9.791%	$245.866	$245.87	$245.85	$245.90
Purchase #7	$38.27	4.633%	$40.043	$40.04	$40.05	$40.00
7 purchase totals =	$579.28		$632.1083	$632.12	$632.10	$632.20