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	$208.71	4.251%	$217.5823	$217.58	$217.60	$217.60
Purchase #2	$105.95	13.480%	$120.2321	$120.23	$120.25	$120.20
Purchase #3	$233.55	13.283%	$264.5724	$264.57	$264.55	$264.60
Purchase #4	$163.72	4.604%	$171.2577	$171.26	$171.25	$171.30
Purchase #5	$200.47	7.737%	$215.9804	$215.98	$216.00	$216.00
Purchase #6	$78.73	12.225%	$88.3547	$88.35	$88.35	$88.40
Purchase #7	$48.41	10.307%	$53.3996	$53.40	$53.40	$53.40
7 purchase totals =	$1,039.54		$1,131.3792	$1,131.37	$1,131.40	$1,131.50