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	$19.37	10.630%	$21.429	$21.43	$21.45	$21.40
Purchase #2	$37.79	13.294%	$42.8138	$42.81	$42.80	$42.80
Purchase #3	$197.93	11.629%	$220.9473	$220.95	$220.95	$220.90
Purchase #4	$126.91	12.482%	$142.7509	$142.75	$142.75	$142.80
Purchase #5	$211.65	5.309%	$222.8865	$222.89	$222.90	$222.90
Purchase #6	$53.89	6.357%	$57.3158	$57.32	$57.30	$57.30
Purchase #7	$36.28	5.631%	$38.3229	$38.32	$38.30	$38.30
7 purchase totals =	$683.82		$746.4662	$746.47	$746.45	$746.40