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	$231.54	3.755%	$240.2343	$240.23	$240.25	$240.20
Purchase #2	$191.71	13.732%	$218.0356	$218.04	$218.05	$218.00
Purchase #3	$108.40	6.330%	$115.2617	$115.26	$115.25	$115.30
Purchase #4	$161.29	8.393%	$174.8271	$174.83	$174.85	$174.80
Purchase #5	$156.85	9.413%	$171.6143	$171.61	$171.60	$171.60
Purchase #6	$147.94	4.277%	$154.2674	$154.27	$154.25	$154.30
Purchase #7	$196.90	13.144%	$222.7805	$222.78	$222.80	$222.80
7 purchase totals =	$1,194.63		$1,297.0209	$1,297.02	$1,297.05	$1,297.00