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	$241.59	3.486%	$250.0118	$250.01	$250.00	$250.00
Purchase #2	$81.77	12.637%	$92.1033	$92.10	$92.10	$92.10
Purchase #3	$91.37	5.202%	$96.1231	$96.12	$96.10	$96.10
Purchase #4	$24.75	11.151%	$27.5099	$27.51	$27.50	$27.50
Purchase #5	$53.31	6.739%	$56.9026	$56.90	$56.90	$56.90
Purchase #6	$168.61	11.391%	$187.8164	$187.82	$187.80	$187.80
Purchase #7	$78.96	11.683%	$88.1849	$88.18	$88.20	$88.20
7 purchase totals =	$740.36		$798.6520	$798.64	$798.60	$798.60