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	$81.74	10.510%	$90.3309	$90.33	$90.35	$90.30
Purchase #2	$127.86	10.800%	$141.6689	$141.67	$141.65	$141.70
Purchase #3	$119.54	9.536%	$130.9393	$130.94	$130.95	$130.90
Purchase #4	$235.93	12.775%	$266.0701	$266.07	$266.05	$266.10
Purchase #5	$144.37	4.273%	$150.5389	$150.54	$150.55	$150.50
Purchase #6	$62.62	12.338%	$70.3461	$70.35	$70.35	$70.30
Purchase #7	$80.64	11.215%	$89.6838	$89.68	$89.70	$89.70
7 purchase totals =	$852.70		$939.5780	$939.58	$939.60	$939.50