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	$36.46	5.519%	$38.4722	$38.47	$38.45	$38.50
Purchase #2	$145.72	11.224%	$162.0756	$162.08	$162.10	$162.10
Purchase #3	$38.85	5.528%	$40.9976	$41.00	$41.00	$41.00
Purchase #4	$126.36	10.234%	$139.2917	$139.29	$139.30	$139.30
Purchase #5	$37.34	10.418%	$41.2301	$41.23	$41.25	$41.20
Purchase #6	$64.43	12.214%	$72.2995	$72.30	$72.30	$72.30
Purchase #7	$73.96	9.571%	$81.0387	$81.04	$81.05	$81.00
7 purchase totals =	$523.12		$575.4054	$575.41	$575.45	$575.40