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	$5.51	4.503%	$5.7581	$5.76	$5.75	$5.80
Purchase #2	$93.70	11.558%	$104.5298	$104.53	$104.55	$104.50
Purchase #3	$19.43	11.145%	$21.5955	$21.60	$21.60	$21.60
Purchase #4	$171.45	11.334%	$190.8821	$190.88	$190.90	$190.90
Purchase #5	$119.48	10.403%	$131.9095	$131.91	$131.90	$131.90
Purchase #6	$129.75	4.461%	$135.5381	$135.54	$135.55	$135.50
Purchase #7	$132.91	13.751%	$151.1865	$151.19	$151.20	$151.20
7 purchase totals =	$672.23		$741.3996	$741.41	$741.45	$741.40