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	$137.56	5.365%	$144.9401	$144.94	$144.95	$144.90
Purchase #2	$103.79	6.608%	$110.6484	$110.65	$110.65	$110.60
Purchase #3	$67.61	6.565%	$72.0486	$72.05	$72.05	$72.00
Purchase #4	$123.49	10.426%	$136.3651	$136.37	$136.35	$136.40
Purchase #5	$103.83	4.526%	$108.5293	$108.53	$108.55	$108.50
Purchase #6	$223.89	6.253%	$237.8898	$237.89	$237.90	$237.90
Purchase #7	$106.29	13.697%	$120.8485	$120.85	$120.85	$120.80
7 purchase totals =	$866.46		$931.2698	$931.28	$931.30	$931.10