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	$37.50	5.472%	$39.552	$39.55	$39.55	$39.60
Purchase #2	$180.27	6.154%	$191.3638	$191.36	$191.35	$191.40
Purchase #3	$99.66	11.392%	$111.0133	$111.01	$111.00	$111.00
Purchase #4	$160.70	13.113%	$181.7726	$181.77	$181.75	$181.80
Purchase #5	$39.94	5.186%	$42.0113	$42.01	$42.00	$42.00
Purchase #6	$93.75	11.793%	$104.8059	$104.81	$104.80	$104.80
Purchase #7	$182.96	7.727%	$197.0973	$197.10	$197.10	$197.10
7 purchase totals =	$794.78		$867.6162	$867.61	$867.55	$867.70