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	$216.85	12.543%	$244.0495	$244.05	$244.05	$244.00
Purchase #2	$87.44	3.524%	$90.5214	$90.52	$90.50	$90.50
Purchase #3	$215.27	11.540%	$240.1122	$240.11	$240.10	$240.10
Purchase #4	$138.92	13.432%	$157.5797	$157.58	$157.60	$157.60
Purchase #5	$128.35	8.719%	$139.5408	$139.54	$139.55	$139.50
Purchase #6	$185.85	4.236%	$193.7226	$193.72	$193.70	$193.70
Purchase #7	$87.35	3.465%	$90.3767	$90.38	$90.40	$90.40
7 purchase totals =	$1,060.03		$1,155.9029	$1,155.90	$1,155.90	$1,155.80