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	$142.76	3.163%	$147.2755	$147.28	$147.30	$147.30
Purchase #2	$7.30	8.167%	$7.8962	$7.90	$7.90	$7.90
Purchase #3	$206.38	11.830%	$230.7948	$230.79	$230.80	$230.80
Purchase #4	$164.35	6.483%	$175.0048	$175.00	$175.00	$175.00
Purchase #5	$10.86	4.450%	$11.3433	$11.34	$11.35	$11.30
Purchase #6	$112.95	9.407%	$123.5752	$123.58	$123.60	$123.60
Purchase #7	$130.56	9.781%	$143.3301	$143.33	$143.35	$143.30
7 purchase totals =	$775.16		$839.2199	$839.22	$839.30	$839.20