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	$18.86	7.441%	$20.2634	$20.26	$20.25	$20.30
Purchase #2	$221.28	10.783%	$245.1406	$245.14	$245.15	$245.10
Purchase #3	$121.54	5.723%	$128.4957	$128.50	$128.50	$128.50
Purchase #4	$201.59	11.256%	$224.281	$224.28	$224.30	$224.30
Purchase #5	$11.97	4.472%	$12.5053	$12.51	$12.50	$12.50
Purchase #6	$85.59	12.607%	$96.3803	$96.38	$96.40	$96.40
Purchase #7	$11.50	7.561%	$12.3695	$12.37	$12.35	$12.40
7 purchase totals =	$672.33		$739.4358	$739.44	$739.45	$739.50