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	$18.33	10.867%	$20.3219	$20.32	$20.30	$20.30
Purchase #2	$111.37	7.594%	$119.8274	$119.83	$119.85	$119.80
Purchase #3	$242.76	3.126%	$250.3487	$250.35	$250.35	$250.30
Purchase #4	$119.65	9.330%	$130.8133	$130.81	$130.80	$130.80
Purchase #5	$130.56	13.467%	$148.1425	$148.14	$148.15	$148.10
Purchase #6	$180.97	8.518%	$196.385	$196.39	$196.40	$196.40
Purchase #7	$155.73	6.360%	$165.6344	$165.63	$165.65	$165.60
7 purchase totals =	$959.37		$1,031.4732	$1,031.47	$1,031.50	$1,031.30