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	$170.99	7.539%	$183.8809	$183.88	$183.90	$183.90
Purchase #2	$243.63	7.388%	$261.6294	$261.63	$261.65	$261.60
Purchase #3	$169.90	5.359%	$179.0049	$179.00	$179.00	$179.00
Purchase #4	$59.98	9.848%	$65.8868	$65.89	$65.90	$65.90
Purchase #5	$104.52	11.803%	$116.8565	$116.86	$116.85	$116.90
Purchase #6	$28.25	11.815%	$31.5877	$31.59	$31.60	$31.60
Purchase #7	$159.69	4.576%	$166.9974	$167.00	$167.00	$167.00
7 purchase totals =	$936.96		$1,005.8436	$1,005.85	$1,005.90	$1,005.90