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	$34.73	13.399%	$39.3835	$39.38	$39.40	$39.40
Purchase #2	$72.36	8.246%	$78.3268	$78.33	$78.35	$78.30
Purchase #3	$219.30	6.486%	$233.5238	$233.52	$233.50	$233.50
Purchase #4	$12.75	4.117%	$13.2749	$13.27	$13.25	$13.30
Purchase #5	$150.77	7.515%	$162.1004	$162.10	$162.10	$162.10
Purchase #6	$199.29	8.307%	$215.845	$215.85	$215.85	$215.80
Purchase #7	$50.75	11.424%	$56.5477	$56.55	$56.55	$56.50
7 purchase totals =	$739.95		$799.0021	$799.00	$799.00	$798.90