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	$60.51	11.638%	$67.5522	$67.55	$67.55	$67.60
Purchase #2	$43.28	8.409%	$46.9194	$46.92	$46.90	$46.90
Purchase #3	$155.43	9.758%	$170.5969	$170.60	$170.60	$170.60
Purchase #4	$82.58	7.636%	$88.8858	$88.89	$88.90	$88.90
Purchase #5	$228.40	9.414%	$249.9016	$249.90	$249.90	$249.90
Purchase #6	$71.89	13.465%	$81.57	$81.57	$81.55	$81.60
Purchase #7	$240.45	11.719%	$268.6283	$268.63	$268.65	$268.60
7 purchase totals =	$882.54		$974.0542	$974.06	$974.05	$974.10