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	$29.88	10.174%	$32.92	$32.92	$32.90	$32.90
Purchase #2	$82.88	8.739%	$90.1229	$90.12	$90.10	$90.10
Purchase #3	$78.33	6.228%	$83.2084	$83.21	$83.20	$83.20
Purchase #4	$243.96	6.359%	$259.4734	$259.47	$259.45	$259.50
Purchase #5	$174.58	12.633%	$196.6347	$196.63	$196.65	$196.60
Purchase #6	$122.86	13.359%	$139.2729	$139.27	$139.25	$139.30
Purchase #7	$161.27	12.356%	$181.1965	$181.20	$181.20	$181.20
7 purchase totals =	$893.76		$982.8288	$982.82	$982.75	$982.80