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	$5.60	6.354%	$5.9558	$5.96	$5.95	$6.00
Purchase #2	$172.46	7.738%	$185.805	$185.81	$185.80	$185.80
Purchase #3	$115.87	3.168%	$119.5408	$119.54	$119.55	$119.50
Purchase #4	$91.56	6.327%	$97.353	$97.35	$97.35	$97.40
Purchase #5	$248.37	11.331%	$276.5128	$276.51	$276.50	$276.50
Purchase #6	$121.54	13.362%	$137.7802	$137.78	$137.80	$137.80
Purchase #7	$182.31	4.516%	$190.5431	$190.54	$190.55	$190.50
7 purchase totals =	$937.71		$1,013.4907	$1,013.49	$1,013.50	$1,013.50