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	$104.81	10.294%	$115.5991	$115.60	$115.60	$115.60
Purchase #2	$81.94	6.858%	$87.5594	$87.56	$87.55	$87.60
Purchase #3	$119.72	12.410%	$134.5773	$134.58	$134.60	$134.60
Purchase #4	$71.49	9.815%	$78.5067	$78.51	$78.50	$78.50
Purchase #5	$146.52	12.220%	$164.4247	$164.42	$164.40	$164.40
Purchase #6	$91.26	5.722%	$96.4819	$96.48	$96.50	$96.50
Purchase #7	$72.88	10.192%	$80.3079	$80.31	$80.30	$80.30
7 purchase totals =	$688.62		$757.4570	$757.46	$757.45	$757.50