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	$184.53	8.586%	$200.3737	$200.37	$200.35	$200.40
Purchase #2	$157.70	8.570%	$171.2149	$171.21	$171.20	$171.20
Purchase #3	$77.95	10.747%	$86.3273	$86.33	$86.35	$86.30
Purchase #4	$177.98	11.383%	$198.2395	$198.24	$198.25	$198.20
Purchase #5	$100.84	10.282%	$111.2084	$111.21	$111.20	$111.20
Purchase #6	$16.43	12.294%	$18.4499	$18.45	$18.45	$18.40
Purchase #7	$36.51	6.266%	$38.7977	$38.80	$38.80	$38.80
7 purchase totals =	$751.94		$824.6114	$824.61	$824.60	$824.50