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	$18.89	12.278%	$21.2093	$21.21	$21.20	$21.20
Purchase #2	$142.79	13.464%	$162.0152	$162.02	$162.00	$162.00
Purchase #3	$10.72	4.767%	$11.231	$11.23	$11.25	$11.20
Purchase #4	$54.61	5.520%	$57.6245	$57.62	$57.60	$57.60
Purchase #5	$191.85	13.831%	$218.3848	$218.38	$218.40	$218.40
Purchase #6	$31.86	13.546%	$36.1758	$36.18	$36.20	$36.20
Purchase #7	$136.36	10.231%	$150.311	$150.31	$150.30	$150.30
7 purchase totals =	$587.08		$656.9516	$656.95	$656.95	$656.90