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	$168.72	9.734%	$185.1432	$185.14	$185.15	$185.10
Purchase #2	$96.77	6.632%	$103.1878	$103.19	$103.20	$103.20
Purchase #3	$243.35	11.208%	$270.6247	$270.62	$270.60	$270.60
Purchase #4	$69.60	10.648%	$77.011	$77.01	$77.00	$77.00
Purchase #5	$183.96	3.235%	$189.9111	$189.91	$189.90	$189.90
Purchase #6	$42.26	12.105%	$47.3756	$47.38	$47.40	$47.40
Purchase #7	$241.38	11.132%	$268.2504	$268.25	$268.25	$268.30
7 purchase totals =	$1,046.04		$1,141.5038	$1,141.50	$1,141.50	$1,141.50