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	$171.80	5.275%	$180.8625	$180.86	$180.85	$180.90
Purchase #2	$36.81	10.198%	$40.5639	$40.56	$40.55	$40.60
Purchase #3	$239.80	6.348%	$255.0225	$255.02	$255.00	$255.00
Purchase #4	$43.52	3.405%	$45.0019	$45.00	$45.00	$45.00
Purchase #5	$27.28	11.403%	$30.3907	$30.39	$30.40	$30.40
Purchase #6	$200.77	13.633%	$228.141	$228.14	$228.15	$228.10
Purchase #7	$80.90	9.161%	$88.3112	$88.31	$88.30	$88.30
7 purchase totals =	$800.88		$868.2937	$868.28	$868.25	$868.30