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	$241.44	12.219%	$270.9416	$270.94	$270.95	$270.90
Purchase #2	$81.53	9.765%	$89.4914	$89.49	$89.50	$89.50
Purchase #3	$176.86	11.112%	$196.5127	$196.51	$196.50	$196.50
Purchase #4	$230.59	6.786%	$246.2378	$246.24	$246.25	$246.20
Purchase #5	$20.72	9.217%	$22.6298	$22.63	$22.65	$22.60
Purchase #6	$181.60	3.321%	$187.6309	$187.63	$187.65	$187.60
Purchase #7	$177.91	5.389%	$187.4976	$187.50	$187.50	$187.50
7 purchase totals =	$1,110.65		$1,200.9418	$1,200.94	$1,201.00	$1,200.80