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	$27.49	4.508%	$28.7292	$28.73	$28.75	$28.70
Purchase #2	$113.54	12.633%	$127.8835	$127.88	$127.90	$127.90
Purchase #3	$97.85	3.184%	$100.9655	$100.97	$100.95	$101.00
Purchase #4	$39.73	11.571%	$44.3272	$44.33	$44.35	$44.30
Purchase #5	$7.63	9.237%	$8.3348	$8.33	$8.35	$8.30
Purchase #6	$9.89	10.443%	$10.9228	$10.92	$10.90	$10.90
Purchase #7	$162.25	13.241%	$183.7335	$183.73	$183.75	$183.70
7 purchase totals =	$458.38		$504.8965	$504.89	$504.95	$504.80