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	$128.78	6.772%	$137.501	$137.50	$137.50	$137.50
Purchase #2	$24.95	8.776%	$27.1396	$27.14	$27.15	$27.10
Purchase #3	$237.83	7.359%	$255.3319	$255.33	$255.35	$255.30
Purchase #4	$161.36	13.761%	$183.5647	$183.56	$183.55	$183.60
Purchase #5	$231.31	9.403%	$253.0601	$253.06	$253.05	$253.10
Purchase #6	$62.50	13.419%	$70.8869	$70.89	$70.90	$70.90
Purchase #7	$81.81	8.193%	$88.5127	$88.51	$88.50	$88.50
7 purchase totals =	$928.54		$1,015.9969	$1,015.99	$1,016.00	$1,016.00