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	$202.67	7.717%	$218.31	$218.31	$218.30	$218.30
Purchase #2	$69.96	12.527%	$78.7239	$78.72	$78.70	$78.70
Purchase #3	$202.60	5.446%	$213.6336	$213.63	$213.65	$213.60
Purchase #4	$107.39	11.550%	$119.7935	$119.79	$119.80	$119.80
Purchase #5	$109.30	8.362%	$118.4397	$118.44	$118.45	$118.40
Purchase #6	$72.58	10.841%	$80.4484	$80.45	$80.45	$80.40
Purchase #7	$38.56	12.273%	$43.2925	$43.29	$43.30	$43.30
7 purchase totals =	$803.06		$872.6416	$872.63	$872.65	$872.50