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	$130.46	10.435%	$144.0735	$144.07	$144.05	$144.10
Purchase #2	$34.96	7.218%	$37.4834	$37.48	$37.50	$37.50
Purchase #3	$10.66	4.243%	$11.1123	$11.11	$11.10	$11.10
Purchase #4	$220.67	13.484%	$250.4251	$250.43	$250.45	$250.40
Purchase #5	$87.90	4.126%	$91.5268	$91.53	$91.55	$91.50
Purchase #6	$142.36	11.329%	$158.488	$158.49	$158.50	$158.50
Purchase #7	$133.45	6.492%	$142.1136	$142.11	$142.10	$142.10
7 purchase totals =	$760.46		$835.2227	$835.22	$835.25	$835.20