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	$27.90	5.411%	$29.4097	$29.41	$29.40	$29.40
Purchase #2	$83.95	8.458%	$91.0505	$91.05	$91.05	$91.10
Purchase #3	$14.59	6.391%	$15.5224	$15.52	$15.50	$15.50
Purchase #4	$70.82	10.740%	$78.4261	$78.43	$78.45	$78.40
Purchase #5	$43.68	5.269%	$45.9815	$45.98	$46.00	$46.00
Purchase #6	$210.35	13.132%	$237.9732	$237.97	$237.95	$238.00
Purchase #7	$98.35	7.628%	$105.8521	$105.85	$105.85	$105.90
7 purchase totals =	$549.64		$604.2155	$604.21	$604.20	$604.30