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	$241.83	12.436%	$271.904	$271.90	$271.90	$271.90
Purchase #2	$65.36	3.331%	$67.5371	$67.54	$67.55	$67.50
Purchase #3	$96.39	9.871%	$105.9047	$105.90	$105.90	$105.90
Purchase #4	$21.50	12.544%	$24.197	$24.20	$24.20	$24.20
Purchase #5	$226.84	7.488%	$243.8258	$243.83	$243.85	$243.80
Purchase #6	$53.28	3.381%	$55.0814	$55.08	$55.10	$55.10
Purchase #7	$199.92	12.595%	$225.0999	$225.10	$225.10	$225.10
7 purchase totals =	$905.12		$993.5499	$993.55	$993.60	$993.50