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	$81.56	5.315%	$85.8949	$85.89	$85.90	$85.90
Purchase #2	$222.77	12.690%	$251.0395	$251.04	$251.05	$251.00
Purchase #3	$38.53	10.372%	$42.5263	$42.53	$42.55	$42.50
Purchase #4	$241.66	12.731%	$272.4257	$272.43	$272.45	$272.40
Purchase #5	$191.92	6.751%	$204.8765	$204.88	$204.90	$204.90
Purchase #6	$61.96	12.365%	$69.6214	$69.62	$69.60	$69.60
Purchase #7	$189.79	5.662%	$200.5359	$200.54	$200.55	$200.50
7 purchase totals =	$1,028.19		$1,126.9202	$1,126.93	$1,127.00	$1,126.80