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	$175.51	5.330%	$184.8647	$184.86	$184.85	$184.90
Purchase #2	$39.60	12.595%	$44.5876	$44.59	$44.60	$44.60
Purchase #3	$196.78	11.593%	$219.5927	$219.59	$219.60	$219.60
Purchase #4	$182.65	3.520%	$189.0793	$189.08	$189.10	$189.10
Purchase #5	$198.84	5.784%	$210.3409	$210.34	$210.35	$210.30
Purchase #6	$102.89	9.621%	$112.789	$112.79	$112.80	$112.80
Purchase #7	$120.82	6.208%	$128.3205	$128.32	$128.30	$128.30
7 purchase totals =	$1,017.09		$1,089.5747	$1,089.57	$1,089.60	$1,089.60