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	$244.26	13.872%	$278.1437	$278.14	$278.15	$278.10
Purchase #2	$55.78	6.812%	$59.5797	$59.58	$59.60	$59.60
Purchase #3	$161.48	13.622%	$183.4768	$183.48	$183.50	$183.50
Purchase #4	$102.84	6.175%	$109.1904	$109.19	$109.20	$109.20
Purchase #5	$75.74	8.824%	$82.4233	$82.42	$82.40	$82.40
Purchase #6	$240.41	5.257%	$253.0484	$253.05	$253.05	$253.00
Purchase #7	$33.74	6.859%	$36.0542	$36.05	$36.05	$36.10
7 purchase totals =	$914.25		$1,001.9165	$1,001.91	$1,001.95	$1,001.90