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	$177.40	6.780%	$189.4277	$189.43	$189.45	$189.40
Purchase #2	$39.59	7.376%	$42.5102	$42.51	$42.50	$42.50
Purchase #3	$186.67	5.162%	$196.3059	$196.31	$196.30	$196.30
Purchase #4	$82.43	11.688%	$92.0644	$92.06	$92.05	$92.10
Purchase #5	$150.43	11.846%	$168.2499	$168.25	$168.25	$168.20
Purchase #6	$7.87	11.295%	$8.7589	$8.76	$8.75	$8.80
Purchase #7	$185.43	7.753%	$199.8064	$199.81	$199.80	$199.80
7 purchase totals =	$829.82		$897.1234	$897.13	$897.10	$897.10