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	$250.77	11.200%	$278.8562	$278.86	$278.85	$278.90
Purchase #2	$202.81	8.256%	$219.554	$219.55	$219.55	$219.60
Purchase #3	$80.76	3.531%	$83.6116	$83.61	$83.60	$83.60
Purchase #4	$197.53	12.678%	$222.5729	$222.57	$222.55	$222.60
Purchase #5	$47.50	6.534%	$50.6037	$50.60	$50.60	$50.60
Purchase #6	$67.50	5.235%	$71.0336	$71.03	$71.05	$71.00
Purchase #7	$166.96	4.171%	$173.9239	$173.92	$173.90	$173.90
7 purchase totals =	$1,013.83		$1,100.1559	$1,100.14	$1,100.10	$1,100.20