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	$99.36	12.246%	$111.5276	$111.53	$111.55	$111.50
Purchase #2	$25.79	10.655%	$28.5379	$28.54	$28.55	$28.50
Purchase #3	$95.43	13.873%	$108.669	$108.67	$108.65	$108.70
Purchase #4	$85.80	10.632%	$94.9223	$94.92	$94.90	$94.90
Purchase #5	$145.75	13.532%	$165.4729	$165.47	$165.45	$165.50
Purchase #6	$82.39	7.434%	$88.5149	$88.51	$88.50	$88.50
Purchase #7	$232.34	10.711%	$257.2259	$257.23	$257.25	$257.20
7 purchase totals =	$766.86		$854.8705	$854.87	$854.85	$854.80