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	$28.30	11.796%	$31.6383	$31.64	$31.65	$31.60
Purchase #2	$87.64	13.109%	$99.1287	$99.13	$99.15	$99.10
Purchase #3	$38.95	6.280%	$41.3961	$41.40	$41.40	$41.40
Purchase #4	$43.76	3.562%	$45.3187	$45.32	$45.30	$45.30
Purchase #5	$168.62	9.258%	$184.2308	$184.23	$184.25	$184.20
Purchase #6	$144.53	9.461%	$158.204	$158.20	$158.20	$158.20
Purchase #7	$214.71	12.587%	$241.7355	$241.74	$241.75	$241.70
7 purchase totals =	$726.51		$801.6521	$801.66	$801.70	$801.50