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	$159.76	6.169%	$169.6156	$169.62	$169.60	$169.60
Purchase #2	$73.72	13.715%	$83.8307	$83.83	$83.85	$83.80
Purchase #3	$104.80	11.675%	$117.0354	$117.04	$117.05	$117.00
Purchase #4	$190.85	4.278%	$199.0146	$199.01	$199.00	$199.00
Purchase #5	$81.33	10.132%	$89.5704	$89.57	$89.55	$89.60
Purchase #6	$250.42	8.522%	$271.7608	$271.76	$271.75	$271.80
Purchase #7	$64.25	8.223%	$69.5333	$69.53	$69.55	$69.50
7 purchase totals =	$925.13		$1,000.3608	$1,000.36	$1,000.35	$1,000.30