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	$223.90	11.453%	$249.5433	$249.54	$249.55	$249.50
Purchase #2	$75.76	4.799%	$79.3957	$79.40	$79.40	$79.40
Purchase #3	$15.70	4.320%	$16.3782	$16.38	$16.40	$16.40
Purchase #4	$90.83	13.139%	$102.7642	$102.76	$102.75	$102.80
Purchase #5	$159.80	11.702%	$178.4998	$178.50	$178.50	$178.50
Purchase #6	$207.53	7.756%	$223.626	$223.63	$223.65	$223.60
Purchase #7	$114.25	12.332%	$128.3393	$128.34	$128.35	$128.30
7 purchase totals =	$887.77		$978.5465	$978.55	$978.60	$978.50