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	$26.91	5.433%	$28.372	$28.37	$28.35	$28.40
Purchase #2	$138.57	6.165%	$147.1128	$147.11	$147.10	$147.10
Purchase #3	$80.36	12.307%	$90.2499	$90.25	$90.25	$90.20
Purchase #4	$31.78	4.291%	$33.1437	$33.14	$33.15	$33.10
Purchase #5	$151.43	6.611%	$161.441	$161.44	$161.45	$161.40
Purchase #6	$94.68	11.751%	$105.8058	$105.81	$105.80	$105.80
Purchase #7	$43.50	3.172%	$44.8798	$44.88	$44.90	$44.90
7 purchase totals =	$567.23		$611.0050	$611.00	$611.00	$610.90