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	$28.61	10.647%	$31.6561	$31.66	$31.65	$31.70
Purchase #2	$33.31	11.868%	$37.2632	$37.26	$37.25	$37.30
Purchase #3	$170.91	13.190%	$193.453	$193.45	$193.45	$193.50
Purchase #4	$82.42	9.314%	$90.0966	$90.10	$90.10	$90.10
Purchase #5	$188.64	12.441%	$212.1087	$212.11	$212.10	$212.10
Purchase #6	$235.80	9.578%	$258.3849	$258.38	$258.40	$258.40
Purchase #7	$142.50	7.615%	$153.3514	$153.35	$153.35	$153.40
7 purchase totals =	$882.19		$976.3139	$976.31	$976.30	$976.50