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	$32.77	11.726%	$36.6126	$36.61	$36.60	$36.60
Purchase #2	$96.64	9.508%	$105.8285	$105.83	$105.85	$105.80
Purchase #3	$70.73	13.111%	$80.0034	$80.00	$80.00	$80.00
Purchase #4	$126.65	11.801%	$141.596	$141.60	$141.60	$141.60
Purchase #5	$141.84	6.324%	$150.81	$150.81	$150.80	$150.80
Purchase #6	$113.84	13.235%	$128.9067	$128.91	$128.90	$128.90
Purchase #7	$67.62	7.756%	$72.8646	$72.86	$72.85	$72.90
7 purchase totals =	$650.09		$716.6218	$716.62	$716.60	$716.60