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	$240.43	11.628%	$268.3872	$268.39	$268.40	$268.40
Purchase #2	$59.60	12.645%	$67.1364	$67.14	$67.15	$67.10
Purchase #3	$6.30	10.277%	$6.9475	$6.95	$6.95	$6.90
Purchase #4	$98.90	6.682%	$105.5085	$105.51	$105.50	$105.50
Purchase #5	$80.80	11.612%	$90.1825	$90.18	$90.20	$90.20
Purchase #6	$9.48	4.561%	$9.9124	$9.91	$9.90	$9.90
Purchase #7	$155.87	7.484%	$167.5353	$167.54	$167.55	$167.50
7 purchase totals =	$651.38		$715.6098	$715.62	$715.65	$715.50