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	$57.57	4.856%	$60.3656	$60.37	$60.35	$60.40
Purchase #2	$42.53	4.215%	$44.3226	$44.32	$44.30	$44.30
Purchase #3	$146.96	3.573%	$152.2109	$152.21	$152.20	$152.20
Purchase #4	$169.31	9.451%	$185.3115	$185.31	$185.30	$185.30
Purchase #5	$36.85	9.167%	$40.228	$40.23	$40.25	$40.20
Purchase #6	$89.58	8.813%	$97.4747	$97.47	$97.45	$97.50
Purchase #7	$30.34	3.532%	$31.4116	$31.41	$31.40	$31.40
7 purchase totals =	$573.14		$611.3249	$611.32	$611.25	$611.30