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	$38.63	7.455%	$41.5099	$41.51	$41.50	$41.50
Purchase #2	$134.48	10.602%	$148.7376	$148.74	$148.75	$148.70
Purchase #3	$129.41	9.813%	$142.109	$142.11	$142.10	$142.10
Purchase #4	$23.41	7.769%	$25.2287	$25.23	$25.25	$25.20
Purchase #5	$153.72	11.674%	$171.6653	$171.67	$171.65	$171.70
Purchase #6	$83.67	7.786%	$90.1845	$90.18	$90.20	$90.20
Purchase #7	$26.88	9.437%	$29.4167	$29.42	$29.40	$29.40
7 purchase totals =	$590.20		$648.8517	$648.86	$648.85	$648.80