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	$165.37	9.122%	$180.4551	$180.46	$180.45	$180.50
Purchase #2	$72.61	8.676%	$78.9096	$78.91	$78.90	$78.90
Purchase #3	$55.69	11.342%	$62.0064	$62.01	$62.00	$62.00
Purchase #4	$83.47	3.732%	$86.5851	$86.59	$86.60	$86.60
Purchase #5	$58.87	4.626%	$61.5933	$61.59	$61.60	$61.60
Purchase #6	$94.67	12.304%	$106.3182	$106.32	$106.30	$106.30
Purchase #7	$225.56	7.705%	$242.9394	$242.94	$242.95	$242.90
7 purchase totals =	$756.24		$818.8071	$818.82	$818.80	$818.80