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	$30.53	3.578%	$31.6224	$31.62	$31.60	$31.60
Purchase #2	$127.61	12.156%	$143.1223	$143.12	$143.10	$143.10
Purchase #3	$83.61	6.749%	$89.2528	$89.25	$89.25	$89.30
Purchase #4	$97.43	13.192%	$110.283	$110.28	$110.30	$110.30
Purchase #5	$250.55	13.546%	$284.4895	$284.49	$284.50	$284.50
Purchase #6	$29.40	12.468%	$33.0656	$33.07	$33.05	$33.10
Purchase #7	$203.79	9.607%	$223.3681	$223.37	$223.35	$223.40
7 purchase totals =	$822.92		$915.2037	$915.20	$915.15	$915.30