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	$40.31	5.737%	$42.6226	$42.62	$42.60	$42.60
Purchase #2	$77.39	4.516%	$80.8849	$80.88	$80.90	$80.90
Purchase #3	$35.57	10.520%	$39.312	$39.31	$39.30	$39.30
Purchase #4	$89.99	10.858%	$99.7611	$99.76	$99.75	$99.80
Purchase #5	$241.77	9.595%	$264.9678	$264.97	$264.95	$265.00
Purchase #6	$73.73	5.721%	$77.9481	$77.95	$77.95	$77.90
Purchase #7	$44.50	9.370%	$48.6697	$48.67	$48.65	$48.70
7 purchase totals =	$603.26		$654.1662	$654.16	$654.10	$654.20