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	$19.42	12.703%	$21.8869	$21.89	$21.90	$21.90
Purchase #2	$44.93	8.828%	$48.8964	$48.90	$48.90	$48.90
Purchase #3	$90.63	11.676%	$101.212	$101.21	$101.20	$101.20
Purchase #4	$130.35	6.848%	$139.2764	$139.28	$139.30	$139.30
Purchase #5	$116.35	9.458%	$127.3544	$127.35	$127.35	$127.40
Purchase #6	$47.32	12.842%	$53.3968	$53.40	$53.40	$53.40
Purchase #7	$53.59	8.412%	$58.098	$58.10	$58.10	$58.10
7 purchase totals =	$502.59		$550.1209	$550.13	$550.15	$550.20