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	$84.77	13.113%	$95.8859	$95.89	$95.90	$95.90
Purchase #2	$134.55	9.856%	$147.8112	$147.81	$147.80	$147.80
Purchase #3	$87.63	13.765%	$99.6923	$99.69	$99.70	$99.70
Purchase #4	$89.38	10.829%	$99.059	$99.06	$99.05	$99.10
Purchase #5	$108.27	11.330%	$120.537	$120.54	$120.55	$120.50
Purchase #6	$142.83	11.488%	$159.2383	$159.24	$159.25	$159.20
Purchase #7	$21.68	9.679%	$23.7784	$23.78	$23.80	$23.80
7 purchase totals =	$669.11		$746.0021	$746.01	$746.05	$746.00