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	$174.94	7.800%	$188.5853	$188.59	$188.60	$188.60
Purchase #2	$249.89	12.367%	$280.7939	$280.79	$280.80	$280.80
Purchase #3	$42.89	13.779%	$48.7998	$48.80	$48.80	$48.80
Purchase #4	$136.31	12.366%	$153.1661	$153.17	$153.15	$153.20
Purchase #5	$96.56	4.129%	$100.547	$100.55	$100.55	$100.50
Purchase #6	$47.83	12.511%	$53.814	$53.81	$53.80	$53.80
Purchase #7	$42.28	4.853%	$44.3318	$44.33	$44.35	$44.30
7 purchase totals =	$790.70		$870.0379	$870.04	$870.05	$870.00