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	$66.83	12.250%	$75.0167	$75.02	$75.00	$75.00
Purchase #2	$104.83	11.795%	$117.1947	$117.19	$117.20	$117.20
Purchase #3	$70.62	13.387%	$80.0739	$80.07	$80.05	$80.10
Purchase #4	$53.86	4.370%	$56.2137	$56.21	$56.20	$56.20
Purchase #5	$30.89	4.314%	$32.2226	$32.22	$32.20	$32.20
Purchase #6	$95.41	6.792%	$101.8902	$101.89	$101.90	$101.90
Purchase #7	$38.38	4.382%	$40.0618	$40.06	$40.05	$40.10
7 purchase totals =	$460.82		$502.6736	$502.66	$502.60	$502.70