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	$78.41	5.228%	$82.5093	$82.51	$82.50	$82.50
Purchase #2	$5.47	9.803%	$6.0062	$6.01	$6.00	$6.00
Purchase #3	$49.34	4.249%	$51.4365	$51.44	$51.45	$51.40
Purchase #4	$169.68	7.143%	$181.8002	$181.80	$181.80	$181.80
Purchase #5	$73.32	12.353%	$82.3772	$82.38	$82.40	$82.40
Purchase #6	$194.84	12.652%	$219.4912	$219.49	$219.50	$219.50
Purchase #7	$146.53	12.865%	$165.3811	$165.38	$165.40	$165.40
7 purchase totals =	$717.59		$789.0017	$789.01	$789.05	$789.00