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	$26.64	8.123%	$28.804	$28.80	$28.80	$28.80
Purchase #2	$81.96	9.313%	$89.5929	$89.59	$89.60	$89.60
Purchase #3	$100.29	4.609%	$104.9124	$104.91	$104.90	$104.90
Purchase #4	$130.67	6.642%	$139.3491	$139.35	$139.35	$139.30
Purchase #5	$7.46	3.489%	$7.7203	$7.72	$7.70	$7.70
Purchase #6	$215.62	9.385%	$235.8559	$235.86	$235.85	$235.90
Purchase #7	$10.77	9.455%	$11.7883	$11.79	$11.80	$11.80
7 purchase totals =	$573.41		$618.0229	$618.02	$618.00	$618.00