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	$85.73	4.341%	$89.4515	$89.45	$89.45	$89.50
Purchase #2	$97.88	12.177%	$109.7988	$109.80	$109.80	$109.80
Purchase #3	$178.38	6.311%	$189.6376	$189.64	$189.65	$189.60
Purchase #4	$36.44	9.425%	$39.8745	$39.87	$39.85	$39.90
Purchase #5	$176.79	3.810%	$183.5257	$183.53	$183.55	$183.50
Purchase #6	$38.53	13.810%	$43.851	$43.85	$43.85	$43.90
Purchase #7	$166.49	13.639%	$189.1976	$189.20	$189.20	$189.20
7 purchase totals =	$780.24		$845.3367	$845.34	$845.35	$845.40