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	$144.62	12.242%	$162.3244	$162.32	$162.30	$162.30
Purchase #2	$223.38	12.180%	$250.5877	$250.59	$250.60	$250.60
Purchase #3	$214.97	3.762%	$223.0572	$223.06	$223.05	$223.10
Purchase #4	$225.48	8.429%	$244.4857	$244.49	$244.50	$244.50
Purchase #5	$68.82	11.822%	$76.9559	$76.96	$76.95	$77.00
Purchase #6	$58.64	3.831%	$60.8865	$60.89	$60.90	$60.90
Purchase #7	$99.62	5.216%	$104.8162	$104.82	$104.80	$104.80
7 purchase totals =	$1,035.53		$1,123.1136	$1,123.13	$1,123.10	$1,123.20