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	$13.98	6.427%	$14.8785	$14.88	$14.90	$14.90
Purchase #2	$85.60	4.405%	$89.3707	$89.37	$89.35	$89.40
Purchase #3	$100.77	4.269%	$105.0719	$105.07	$105.05	$105.10
Purchase #4	$121.36	8.550%	$131.7363	$131.74	$131.75	$131.70
Purchase #5	$139.54	12.164%	$156.5136	$156.51	$156.50	$156.50
Purchase #6	$160.51	8.351%	$173.9142	$173.91	$173.90	$173.90
Purchase #7	$163.43	3.154%	$168.5846	$168.58	$168.60	$168.60
7 purchase totals =	$785.19		$840.0698	$840.06	$840.05	$840.10