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	$222.59	8.144%	$240.7177	$240.72	$240.70	$240.70
Purchase #2	$19.40	8.734%	$21.0944	$21.09	$21.10	$21.10
Purchase #3	$200.90	7.566%	$216.1001	$216.10	$216.10	$216.10
Purchase #4	$39.40	7.282%	$42.2691	$42.27	$42.25	$42.30
Purchase #5	$13.34	3.567%	$13.8158	$13.82	$13.80	$13.80
Purchase #6	$128.72	10.226%	$141.8829	$141.88	$141.90	$141.90
Purchase #7	$248.57	6.189%	$263.954	$263.95	$263.95	$264.00
7 purchase totals =	$872.92		$939.8340	$939.83	$939.80	$939.90