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	$38.67	8.403%	$41.9194	$41.92	$41.90	$41.90
Purchase #2	$42.85	5.504%	$45.2085	$45.21	$45.20	$45.20
Purchase #3	$61.32	9.270%	$67.0044	$67.00	$67.00	$67.00
Purchase #4	$86.68	5.119%	$91.1171	$91.12	$91.10	$91.10
Purchase #5	$153.70	7.440%	$165.1353	$165.14	$165.15	$165.10
Purchase #6	$82.28	12.224%	$92.3379	$92.34	$92.35	$92.30
Purchase #7	$40.96	6.857%	$43.7686	$43.77	$43.75	$43.80
7 purchase totals =	$506.46		$546.4912	$546.50	$546.45	$546.40