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	$72.79	7.671%	$78.3737	$78.37	$78.35	$78.40
Purchase #2	$37.94	12.402%	$42.6453	$42.65	$42.65	$42.60
Purchase #3	$178.32	12.477%	$200.569	$200.57	$200.55	$200.60
Purchase #4	$37.81	8.433%	$40.9985	$41.00	$41.00	$41.00
Purchase #5	$28.76	11.348%	$32.0237	$32.02	$32.00	$32.00
Purchase #6	$210.39	4.775%	$220.4361	$220.44	$220.45	$220.40
Purchase #7	$46.75	9.530%	$51.2053	$51.21	$51.20	$51.20
7 purchase totals =	$612.76		$666.2516	$666.26	$666.20	$666.20