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	$149.71	3.155%	$154.4334	$154.43	$154.45	$154.40
Purchase #2	$223.97	7.836%	$241.5203	$241.52	$241.50	$241.50
Purchase #3	$124.90	13.800%	$142.1362	$142.14	$142.15	$142.10
Purchase #4	$21.83	11.331%	$24.3036	$24.30	$24.30	$24.30
Purchase #5	$70.47	12.682%	$79.407	$79.41	$79.40	$79.40
Purchase #6	$68.92	4.670%	$72.1386	$72.14	$72.15	$72.10
Purchase #7	$38.51	7.472%	$41.3875	$41.39	$41.40	$41.40
7 purchase totals =	$698.31		$755.3266	$755.33	$755.35	$755.20