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	$79.29	8.869%	$86.3222	$86.32	$86.30	$86.30
Purchase #2	$159.77	10.725%	$176.9053	$176.91	$176.90	$176.90
Purchase #3	$85.49	6.159%	$90.7553	$90.76	$90.75	$90.80
Purchase #4	$41.85	9.639%	$45.8839	$45.88	$45.90	$45.90
Purchase #5	$11.65	6.540%	$12.4119	$12.41	$12.40	$12.40
Purchase #6	$134.88	3.715%	$139.8908	$139.89	$139.90	$139.90
Purchase #7	$33.73	13.711%	$38.3547	$38.35	$38.35	$38.40
7 purchase totals =	$546.66		$590.5241	$590.52	$590.50	$590.60