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	$175.99	4.185%	$183.3552	$183.36	$183.35	$183.40
Purchase #2	$79.59	11.187%	$88.4937	$88.49	$88.50	$88.50
Purchase #3	$125.45	9.558%	$137.4405	$137.44	$137.45	$137.40
Purchase #4	$129.98	9.664%	$142.5413	$142.54	$142.55	$142.50
Purchase #5	$56.53	5.451%	$59.6115	$59.61	$59.60	$59.60
Purchase #6	$232.41	11.523%	$259.1906	$259.19	$259.20	$259.20
Purchase #7	$216.98	5.477%	$228.864	$228.86	$228.85	$228.90
7 purchase totals =	$1,016.93		$1,099.4968	$1,099.49	$1,099.50	$1,099.50