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	$41.27	3.447%	$42.6926	$42.69	$42.70	$42.70
Purchase #2	$196.62	6.487%	$209.3747	$209.37	$209.35	$209.40
Purchase #3	$134.58	4.264%	$140.3185	$140.32	$140.30	$140.30
Purchase #4	$36.94	10.504%	$40.8202	$40.82	$40.80	$40.80
Purchase #5	$56.75	8.866%	$61.7815	$61.78	$61.80	$61.80
Purchase #6	$25.96	8.661%	$28.2084	$28.21	$28.20	$28.20
Purchase #7	$59.91	12.800%	$67.5785	$67.58	$67.60	$67.60
7 purchase totals =	$552.03		$590.7744	$590.77	$590.75	$590.80