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	$219.68	8.385%	$238.1002	$238.10	$238.10	$238.10
Purchase #2	$98.72	9.807%	$108.4015	$108.40	$108.40	$108.40
Purchase #3	$231.67	9.252%	$253.1041	$253.10	$253.10	$253.10
Purchase #4	$240.47	3.481%	$248.8408	$248.84	$248.85	$248.80
Purchase #5	$89.48	9.693%	$98.1533	$98.15	$98.15	$98.20
Purchase #6	$84.75	7.191%	$90.8444	$90.84	$90.85	$90.80
Purchase #7	$40.57	9.435%	$44.3978	$44.40	$44.40	$44.40
7 purchase totals =	$1,005.34		$1,081.8421	$1,081.83	$1,081.85	$1,081.80