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	$68.57	13.409%	$77.7646	$77.76	$77.75	$77.80
Purchase #2	$172.54	9.449%	$188.8433	$188.84	$188.85	$188.80
Purchase #3	$156.89	8.117%	$169.6248	$169.62	$169.60	$169.60
Purchase #4	$169.61	9.539%	$185.7891	$185.79	$185.80	$185.80
Purchase #5	$42.89	12.166%	$48.108	$48.11	$48.10	$48.10
Purchase #6	$83.30	5.697%	$88.0456	$88.05	$88.05	$88.00
Purchase #7	$98.78	13.763%	$112.3751	$112.38	$112.40	$112.40
7 purchase totals =	$792.58		$870.5505	$870.55	$870.55	$870.50