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	$165.43	9.849%	$181.7232	$181.72	$181.70	$181.70
Purchase #2	$24.82	10.705%	$27.477	$27.48	$27.50	$27.50
Purchase #3	$163.27	11.186%	$181.5334	$181.53	$181.55	$181.50
Purchase #4	$211.50	11.759%	$236.3703	$236.37	$236.35	$236.40
Purchase #5	$96.73	4.665%	$101.2425	$101.24	$101.25	$101.20
Purchase #6	$40.74	4.335%	$42.5061	$42.51	$42.50	$42.50
Purchase #7	$124.90	11.316%	$139.0337	$139.03	$139.05	$139.00
7 purchase totals =	$827.39		$909.8862	$909.88	$909.90	$909.80