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	$75.54	6.519%	$80.4645	$80.46	$80.45	$80.50
Purchase #2	$78.29	13.513%	$88.8693	$88.87	$88.85	$88.90
Purchase #3	$54.48	9.251%	$59.5199	$59.52	$59.50	$59.50
Purchase #4	$84.45	11.144%	$93.8611	$93.86	$93.85	$93.90
Purchase #5	$186.30	6.759%	$198.892	$198.89	$198.90	$198.90
Purchase #6	$177.98	7.421%	$191.1879	$191.19	$191.20	$191.20
Purchase #7	$217.46	6.135%	$230.8012	$230.80	$230.80	$230.80
7 purchase totals =	$874.50		$943.5959	$943.59	$943.55	$943.70