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	$171.58	10.646%	$189.8464	$189.85	$189.85	$189.80
Purchase #2	$118.92	7.393%	$127.7118	$127.71	$127.70	$127.70
Purchase #3	$54.78	12.150%	$61.4358	$61.44	$61.45	$61.40
Purchase #4	$155.96	5.371%	$164.3366	$164.34	$164.35	$164.30
Purchase #5	$58.73	8.822%	$63.9112	$63.91	$63.90	$63.90
Purchase #6	$148.30	13.269%	$167.9779	$167.98	$168.00	$168.00
Purchase #7	$89.71	8.532%	$97.3641	$97.36	$97.35	$97.40
7 purchase totals =	$797.98		$872.5838	$872.59	$872.60	$872.50