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	$25.89	9.631%	$28.3835	$28.38	$28.40	$28.40
Purchase #2	$237.85	9.264%	$259.8844	$259.88	$259.90	$259.90
Purchase #3	$47.28	12.669%	$53.2699	$53.27	$53.25	$53.30
Purchase #4	$195.51	7.820%	$210.7989	$210.80	$210.80	$210.80
Purchase #5	$178.59	7.483%	$191.9539	$191.95	$191.95	$192.00
Purchase #6	$79.38	4.486%	$82.941	$82.94	$82.95	$82.90
Purchase #7	$172.65	10.660%	$191.0545	$191.05	$191.05	$191.10
7 purchase totals =	$937.15		$1,018.2861	$1,018.27	$1,018.30	$1,018.40