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	$36.45	8.588%	$39.5803	$39.58	$39.60	$39.60
Purchase #2	$171.76	5.524%	$181.248	$181.25	$181.25	$181.20
Purchase #3	$205.61	12.755%	$231.8356	$231.84	$231.85	$231.80
Purchase #4	$175.61	3.839%	$182.3517	$182.35	$182.35	$182.40
Purchase #5	$211.92	5.635%	$223.8617	$223.86	$223.85	$223.90
Purchase #6	$113.90	4.728%	$119.2852	$119.29	$119.30	$119.30
Purchase #7	$41.73	12.343%	$46.8807	$46.88	$46.90	$46.90
7 purchase totals =	$956.98		$1,025.0432	$1,025.05	$1,025.10	$1,025.10