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	$159.96	4.234%	$166.7327	$166.73	$166.75	$166.70
Purchase #2	$174.85	4.265%	$182.3074	$182.31	$182.30	$182.30
Purchase #3	$50.48	3.373%	$52.1827	$52.18	$52.20	$52.20
Purchase #4	$125.93	11.640%	$140.5883	$140.59	$140.60	$140.60
Purchase #5	$135.99	4.320%	$141.8648	$141.86	$141.85	$141.90
Purchase #6	$39.30	10.766%	$43.531	$43.53	$43.55	$43.50
Purchase #7	$91.65	12.593%	$103.1915	$103.19	$103.20	$103.20
7 purchase totals =	$778.16		$830.3984	$830.39	$830.45	$830.40