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	$48.48	4.588%	$50.7043	$50.70	$50.70	$50.70
Purchase #2	$242.58	12.787%	$273.5987	$273.60	$273.60	$273.60
Purchase #3	$122.80	7.345%	$131.8197	$131.82	$131.80	$131.80
Purchase #4	$93.43	3.253%	$96.4693	$96.47	$96.45	$96.50
Purchase #5	$181.32	4.837%	$190.0904	$190.09	$190.10	$190.10
Purchase #6	$19.51	9.281%	$21.3207	$21.32	$21.30	$21.30
Purchase #7	$31.44	9.217%	$34.3378	$34.34	$34.35	$34.30
7 purchase totals =	$739.56		$798.3409	$798.34	$798.30	$798.30