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	$136.27	4.378%	$142.2359	$142.24	$142.25	$142.20
Purchase #2	$99.53	12.396%	$111.8677	$111.87	$111.85	$111.90
Purchase #3	$30.61	4.238%	$31.9073	$31.91	$31.90	$31.90
Purchase #4	$100.44	8.558%	$109.0357	$109.04	$109.05	$109.00
Purchase #5	$87.80	6.466%	$93.4771	$93.48	$93.50	$93.50
Purchase #6	$10.51	13.234%	$11.9009	$11.90	$11.90	$11.90
Purchase #7	$64.67	7.499%	$69.5196	$69.52	$69.50	$69.50
7 purchase totals =	$529.83		$569.9442	$569.96	$569.95	$569.90