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	$209.60	4.283%	$218.5772	$218.58	$218.60	$218.60
Purchase #2	$110.38	12.742%	$124.4446	$124.44	$124.45	$124.40
Purchase #3	$161.69	13.425%	$183.3969	$183.40	$183.40	$183.40
Purchase #4	$42.51	10.176%	$46.8358	$46.84	$46.85	$46.80
Purchase #5	$24.78	4.609%	$25.9221	$25.92	$25.90	$25.90
Purchase #6	$40.69	7.833%	$43.8772	$43.88	$43.90	$43.90
Purchase #7	$96.26	3.164%	$99.3057	$99.31	$99.30	$99.30
7 purchase totals =	$685.91		$742.3595	$742.37	$742.40	$742.30