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	$99.67	13.658%	$113.2829	$113.28	$113.30	$113.30
Purchase #2	$38.83	5.206%	$40.8515	$40.85	$40.85	$40.90
Purchase #3	$99.84	9.728%	$109.5524	$109.55	$109.55	$109.60
Purchase #4	$50.67	9.169%	$55.3159	$55.32	$55.30	$55.30
Purchase #5	$63.53	3.425%	$65.7059	$65.71	$65.70	$65.70
Purchase #6	$228.32	5.270%	$240.3525	$240.35	$240.35	$240.40
Purchase #7	$139.45	4.202%	$145.3097	$145.31	$145.30	$145.30
7 purchase totals =	$720.31		$770.3708	$770.37	$770.35	$770.50