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	$6.34	5.709%	$6.702	$6.70	$6.70	$6.70
Purchase #2	$109.90	5.840%	$116.3182	$116.32	$116.30	$116.30
Purchase #3	$100.38	12.454%	$112.8813	$112.88	$112.90	$112.90
Purchase #4	$250.28	11.303%	$278.5691	$278.57	$278.55	$278.60
Purchase #5	$106.77	11.521%	$119.071	$119.07	$119.05	$119.10
Purchase #6	$148.53	12.830%	$167.5864	$167.59	$167.60	$167.60
Purchase #7	$138.39	11.477%	$154.273	$154.27	$154.25	$154.30
7 purchase totals =	$860.59		$955.4010	$955.40	$955.35	$955.50