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	$84.45	4.731%	$88.4453	$88.45	$88.45	$88.40
Purchase #2	$179.49	11.304%	$199.7795	$199.78	$199.80	$199.80
Purchase #3	$56.83	12.299%	$63.8195	$63.82	$63.80	$63.80
Purchase #4	$137.72	4.818%	$144.3553	$144.36	$144.35	$144.40
Purchase #5	$195.30	13.872%	$222.392	$222.39	$222.40	$222.40
Purchase #6	$107.52	11.347%	$119.7203	$119.72	$119.70	$119.70
Purchase #7	$46.69	12.151%	$52.3633	$52.36	$52.35	$52.40
7 purchase totals =	$808.00		$890.8752	$890.88	$890.85	$890.90