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	$57.61	6.578%	$61.3996	$61.40	$61.40	$61.40
Purchase #2	$36.44	6.522%	$38.8166	$38.82	$38.80	$38.80
Purchase #3	$93.40	9.207%	$101.9993	$102.00	$102.00	$102.00
Purchase #4	$40.74	3.389%	$42.1207	$42.12	$42.10	$42.10
Purchase #5	$84.78	5.552%	$89.487	$89.49	$89.50	$89.50
Purchase #6	$200.38	10.331%	$221.0813	$221.08	$221.10	$221.10
Purchase #7	$22.90	7.684%	$24.6596	$24.66	$24.65	$24.70
7 purchase totals =	$536.25		$579.5641	$579.57	$579.55	$579.60