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	$51.29	12.629%	$57.7674	$57.77	$57.75	$57.80
Purchase #2	$38.56	10.809%	$42.728	$42.73	$42.75	$42.70
Purchase #3	$43.29	5.620%	$45.7229	$45.72	$45.70	$45.70
Purchase #4	$84.66	13.838%	$96.3753	$96.38	$96.40	$96.40
Purchase #5	$36.63	5.355%	$38.5915	$38.59	$38.60	$38.60
Purchase #6	$27.92	12.317%	$31.3589	$31.36	$31.35	$31.40
Purchase #7	$243.42	9.297%	$266.0508	$266.05	$266.05	$266.10
7 purchase totals =	$525.77		$578.5948	$578.60	$578.60	$578.70