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	$85.39	6.641%	$91.0607	$91.06	$91.05	$91.10
Purchase #2	$221.53	12.789%	$249.8615	$249.86	$249.85	$249.90
Purchase #3	$204.40	13.477%	$231.947	$231.95	$231.95	$231.90
Purchase #4	$148.55	13.558%	$168.6904	$168.69	$168.70	$168.70
Purchase #5	$126.95	7.598%	$136.5957	$136.60	$136.60	$136.60
Purchase #6	$182.39	12.245%	$204.7237	$204.72	$204.70	$204.70
Purchase #7	$87.28	3.169%	$90.0459	$90.05	$90.05	$90.00
7 purchase totals =	$1,056.49		$1,172.9249	$1,172.93	$1,172.90	$1,172.90