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	$226.89	5.168%	$238.6157	$238.62	$238.60	$238.60
Purchase #2	$189.29	3.644%	$196.1877	$196.19	$196.20	$196.20
Purchase #3	$81.70	9.184%	$89.2033	$89.20	$89.20	$89.20
Purchase #4	$108.72	9.835%	$119.4126	$119.41	$119.40	$119.40
Purchase #5	$198.87	6.166%	$211.1323	$211.13	$211.15	$211.10
Purchase #6	$75.56	6.494%	$80.4669	$80.47	$80.45	$80.50
Purchase #7	$53.96	13.854%	$61.4356	$61.44	$61.45	$61.40
7 purchase totals =	$934.99		$996.4541	$996.46	$996.45	$996.40