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	$75.41	3.728%	$78.2213	$78.22	$78.20	$78.20
Purchase #2	$123.30	8.324%	$133.5635	$133.56	$133.55	$133.60
Purchase #3	$157.95	8.757%	$171.7817	$171.78	$171.80	$171.80
Purchase #4	$176.91	13.279%	$200.4019	$200.40	$200.40	$200.40
Purchase #5	$163.96	10.767%	$181.6136	$181.61	$181.60	$181.60
Purchase #6	$174.45	7.649%	$187.7937	$187.79	$187.80	$187.80
Purchase #7	$180.56	10.465%	$199.4556	$199.46	$199.45	$199.50
7 purchase totals =	$1,052.54		$1,152.8313	$1,152.82	$1,152.80	$1,152.90