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	$240.76	12.396%	$270.6046	$270.60	$270.60	$270.60
Purchase #2	$231.61	9.779%	$254.2591	$254.26	$254.25	$254.30
Purchase #3	$75.93	8.346%	$82.2671	$82.27	$82.25	$82.30
Purchase #4	$195.84	7.318%	$210.1716	$210.17	$210.15	$210.20
Purchase #5	$72.49	4.156%	$75.5027	$75.50	$75.50	$75.50
Purchase #6	$151.76	11.768%	$169.6191	$169.62	$169.60	$169.60
Purchase #7	$96.39	9.812%	$105.8478	$105.85	$105.85	$105.80
7 purchase totals =	$1,064.78		$1,168.2720	$1,168.27	$1,168.20	$1,168.30