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	$76.46	3.249%	$78.9442	$78.94	$78.95	$78.90
Purchase #2	$161.80	3.218%	$167.0067	$167.01	$167.00	$167.00
Purchase #3	$65.45	9.511%	$71.6749	$71.67	$71.65	$71.70
Purchase #4	$31.75	11.331%	$35.3476	$35.35	$35.35	$35.30
Purchase #5	$55.46	9.253%	$60.5917	$60.59	$60.60	$60.60
Purchase #6	$61.97	3.339%	$64.0392	$64.04	$64.05	$64.00
Purchase #7	$192.27	4.325%	$200.5857	$200.59	$200.60	$200.60
7 purchase totals =	$645.16		$678.1900	$678.19	$678.20	$678.10