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	$140.41	4.189%	$146.2918	$146.29	$146.30	$146.30
Purchase #2	$29.86	11.155%	$33.1909	$33.19	$33.20	$33.20
Purchase #3	$172.53	12.702%	$194.4448	$194.44	$194.45	$194.40
Purchase #4	$35.31	3.258%	$36.4604	$36.46	$36.45	$36.50
Purchase #5	$189.87	3.348%	$196.2268	$196.23	$196.25	$196.20
Purchase #6	$108.74	5.107%	$114.2934	$114.29	$114.30	$114.30
Purchase #7	$93.87	7.317%	$100.7385	$100.74	$100.75	$100.70
7 purchase totals =	$770.59		$821.6466	$821.64	$821.70	$821.60