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	$21.66	13.416%	$24.5659	$24.57	$24.55	$24.60
Purchase #2	$78.86	3.606%	$81.7037	$81.70	$81.70	$81.70
Purchase #3	$74.77	10.420%	$82.561	$82.56	$82.55	$82.60
Purchase #4	$67.72	5.104%	$71.1764	$71.18	$71.20	$71.20
Purchase #5	$80.77	5.127%	$84.9111	$84.91	$84.90	$84.90
Purchase #6	$73.49	6.562%	$78.3124	$78.31	$78.30	$78.30
Purchase #7	$100.67	10.609%	$111.3501	$111.35	$111.35	$111.40
7 purchase totals =	$497.94		$534.5806	$534.58	$534.55	$534.70