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	$49.73	6.558%	$52.9913	$52.99	$53.00	$53.00
Purchase #2	$180.59	10.777%	$200.0522	$200.05	$200.05	$200.10
Purchase #3	$179.56	10.749%	$198.8609	$198.86	$198.85	$198.90
Purchase #4	$59.46	3.621%	$61.613	$61.61	$61.60	$61.60
Purchase #5	$72.75	10.659%	$80.5044	$80.50	$80.50	$80.50
Purchase #6	$6.61	7.807%	$7.126	$7.13	$7.15	$7.10
Purchase #7	$42.41	13.340%	$48.0675	$48.07	$48.05	$48.10
7 purchase totals =	$591.11		$649.2153	$649.21	$649.20	$649.30