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	$118.25	8.258%	$128.0151	$128.02	$128.00	$128.00
Purchase #2	$50.56	10.208%	$55.7212	$55.72	$55.70	$55.70
Purchase #3	$64.70	13.295%	$73.3019	$73.30	$73.30	$73.30
Purchase #4	$82.31	9.673%	$90.2718	$90.27	$90.25	$90.30
Purchase #5	$162.70	10.201%	$179.297	$179.30	$179.30	$179.30
Purchase #6	$18.81	5.690%	$19.8803	$19.88	$19.90	$19.90
Purchase #7	$18.28	9.136%	$19.9501	$19.95	$19.95	$20.00
7 purchase totals =	$515.61		$566.4374	$566.44	$566.40	$566.50