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	$157.87	13.640%	$179.4035	$179.40	$179.40	$179.40
Purchase #2	$138.67	8.191%	$150.0285	$150.03	$150.05	$150.00
Purchase #3	$125.68	5.831%	$133.0084	$133.01	$133.00	$133.00
Purchase #4	$55.79	7.605%	$60.0328	$60.03	$60.05	$60.00
Purchase #5	$90.96	9.299%	$99.4184	$99.42	$99.40	$99.40
Purchase #6	$209.80	6.684%	$223.823	$223.82	$223.80	$223.80
Purchase #7	$82.66	3.300%	$85.3878	$85.39	$85.40	$85.40
7 purchase totals =	$861.43		$931.1024	$931.10	$931.10	$931.00