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	$150.39	12.296%	$168.882	$168.88	$168.90	$168.90
Purchase #2	$122.83	4.414%	$128.2517	$128.25	$128.25	$128.30
Purchase #3	$46.97	10.218%	$51.7694	$51.77	$51.75	$51.80
Purchase #4	$159.87	3.172%	$164.9411	$164.94	$164.95	$164.90
Purchase #5	$79.71	3.451%	$82.4608	$82.46	$82.45	$82.50
Purchase #6	$117.88	10.351%	$130.0818	$130.08	$130.10	$130.10
Purchase #7	$93.84	4.761%	$98.3077	$98.31	$98.30	$98.30
7 purchase totals =	$771.49		$824.6945	$824.69	$824.70	$824.80