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	$222.29	12.417%	$249.8917	$249.89	$249.90	$249.90
Purchase #2	$191.39	12.745%	$215.7827	$215.78	$215.80	$215.80
Purchase #3	$153.30	7.784%	$165.2329	$165.23	$165.25	$165.20
Purchase #4	$7.49	4.703%	$7.8423	$7.84	$7.85	$7.80
Purchase #5	$114.78	4.729%	$120.2079	$120.21	$120.20	$120.20
Purchase #6	$179.86	9.167%	$196.3478	$196.35	$196.35	$196.30
Purchase #7	$236.81	9.795%	$260.0055	$260.01	$260.00	$260.00
7 purchase totals =	$1,105.92		$1,215.3108	$1,215.31	$1,215.35	$1,215.20