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	$170.64	10.196%	$188.0385	$188.04	$188.05	$188.00
Purchase #2	$37.67	6.373%	$40.0707	$40.07	$40.05	$40.10
Purchase #3	$177.70	10.678%	$196.6748	$196.67	$196.65	$196.70
Purchase #4	$119.79	7.221%	$128.44	$128.44	$128.45	$128.40
Purchase #5	$38.63	13.355%	$43.789	$43.79	$43.80	$43.80
Purchase #6	$137.32	9.342%	$150.1484	$150.15	$150.15	$150.10
Purchase #7	$42.63	10.205%	$46.9804	$46.98	$47.00	$47.00
7 purchase totals =	$724.38		$794.1418	$794.14	$794.15	$794.10