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	$105.58	10.624%	$116.7968	$116.80	$116.80	$116.80
Purchase #2	$20.57	6.501%	$21.9073	$21.91	$21.90	$21.90
Purchase #3	$231.94	12.682%	$261.3546	$261.35	$261.35	$261.40
Purchase #4	$27.55	13.665%	$31.3147	$31.31	$31.30	$31.30
Purchase #5	$79.27	9.144%	$86.5184	$86.52	$86.50	$86.50
Purchase #6	$40.96	10.409%	$45.2235	$45.22	$45.20	$45.20
Purchase #7	$99.93	10.445%	$110.3677	$110.37	$110.35	$110.40
7 purchase totals =	$605.80		$673.4830	$673.48	$673.40	$673.50