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	$81.32	11.695%	$90.8304	$90.83	$90.85	$90.80
Purchase #2	$228.51	11.332%	$254.4048	$254.40	$254.40	$254.40
Purchase #3	$148.51	10.773%	$164.509	$164.51	$164.50	$164.50
Purchase #4	$39.65	11.473%	$44.199	$44.20	$44.20	$44.20
Purchase #5	$33.70	4.628%	$35.2596	$35.26	$35.25	$35.30
Purchase #6	$89.82	6.318%	$95.4948	$95.49	$95.50	$95.50
Purchase #7	$150.42	12.405%	$169.0796	$169.08	$169.10	$169.10
7 purchase totals =	$771.93		$853.7772	$853.77	$853.80	$853.80