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	$6.73	8.582%	$7.3076	$7.31	$7.30	$7.30
Purchase #2	$69.28	4.149%	$72.1544	$72.15	$72.15	$72.20
Purchase #3	$22.43	13.318%	$25.4172	$25.42	$25.40	$25.40
Purchase #4	$99.66	9.668%	$109.2951	$109.30	$109.30	$109.30
Purchase #5	$249.32	3.643%	$258.4027	$258.40	$258.40	$258.40
Purchase #6	$19.88	6.783%	$21.2285	$21.23	$21.25	$21.20
Purchase #7	$76.50	6.484%	$81.4603	$81.46	$81.45	$81.50
7 purchase totals =	$543.80		$575.2658	$575.27	$575.25	$575.30