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	$33.52	5.325%	$35.3049	$35.30	$35.30	$35.30
Purchase #2	$203.70	6.213%	$216.3559	$216.36	$216.35	$216.40
Purchase #3	$178.60	4.342%	$186.3548	$186.35	$186.35	$186.40
Purchase #4	$12.66	12.311%	$14.2186	$14.22	$14.20	$14.20
Purchase #5	$223.57	9.576%	$244.9791	$244.98	$245.00	$245.00
Purchase #6	$85.58	4.393%	$89.3395	$89.34	$89.35	$89.30
Purchase #7	$127.32	12.639%	$143.412	$143.41	$143.40	$143.40
7 purchase totals =	$864.95		$929.9648	$929.96	$929.95	$930.00