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	$99.36	4.562%	$103.8928	$103.89	$103.90	$103.90
Purchase #2	$181.47	5.576%	$191.5888	$191.59	$191.60	$191.60
Purchase #3	$144.65	9.243%	$158.02	$158.02	$158.00	$158.00
Purchase #4	$224.79	9.410%	$245.9427	$245.94	$245.95	$245.90
Purchase #5	$198.72	6.102%	$210.8459	$210.85	$210.85	$210.80
Purchase #6	$174.42	10.484%	$192.7062	$192.71	$192.70	$192.70
Purchase #7	$63.50	13.815%	$72.2725	$72.27	$72.25	$72.30
7 purchase totals =	$1,086.91		$1,175.2689	$1,175.27	$1,175.25	$1,175.20