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	$76.42	3.345%	$78.9762	$78.98	$79.00	$79.00
Purchase #2	$163.27	6.504%	$173.8891	$173.89	$173.90	$173.90
Purchase #3	$15.78	11.231%	$17.5523	$17.55	$17.55	$17.60
Purchase #4	$143.92	12.478%	$161.8783	$161.88	$161.90	$161.90
Purchase #5	$243.43	3.539%	$252.045	$252.05	$252.05	$252.00
Purchase #6	$236.28	9.423%	$258.5447	$258.54	$258.55	$258.50
Purchase #7	$150.74	11.758%	$168.464	$168.46	$168.45	$168.50
7 purchase totals =	$1,029.84		$1,111.3496	$1,111.35	$1,111.40	$1,111.40