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	$150.46	3.562%	$155.8194	$155.82	$155.80	$155.80
Purchase #2	$38.71	11.168%	$43.0331	$43.03	$43.05	$43.00
Purchase #3	$200.47	4.711%	$209.9141	$209.91	$209.90	$209.90
Purchase #4	$111.43	4.668%	$116.6316	$116.63	$116.65	$116.60
Purchase #5	$127.42	7.811%	$137.3728	$137.37	$137.35	$137.40
Purchase #6	$95.98	4.419%	$100.2214	$100.22	$100.20	$100.20
Purchase #7	$213.55	10.444%	$235.8532	$235.85	$235.85	$235.90
7 purchase totals =	$938.02		$998.8456	$998.83	$998.80	$998.80