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	$81.68	6.213%	$86.7548	$86.75	$86.75	$86.80
Purchase #2	$231.27	3.802%	$240.0629	$240.06	$240.05	$240.10
Purchase #3	$82.86	11.681%	$92.5389	$92.54	$92.55	$92.50
Purchase #4	$103.36	8.124%	$111.757	$111.76	$111.75	$111.80
Purchase #5	$39.93	5.412%	$42.091	$42.09	$42.10	$42.10
Purchase #6	$193.80	3.660%	$200.8931	$200.89	$200.90	$200.90
Purchase #7	$52.60	6.637%	$56.0911	$56.09	$56.10	$56.10
7 purchase totals =	$785.50		$830.1888	$830.18	$830.20	$830.30