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	$138.43	8.844%	$150.6727	$150.67	$150.65	$150.70
Purchase #2	$38.90	11.706%	$43.4536	$43.45	$43.45	$43.50
Purchase #3	$160.34	5.226%	$168.7194	$168.72	$168.70	$168.70
Purchase #4	$159.48	3.862%	$165.6391	$165.64	$165.65	$165.60
Purchase #5	$32.86	7.681%	$35.384	$35.38	$35.40	$35.40
Purchase #6	$162.25	5.282%	$170.82	$170.82	$170.80	$170.80
Purchase #7	$41.67	5.117%	$43.8023	$43.80	$43.80	$43.80
7 purchase totals =	$733.93		$778.4911	$778.48	$778.45	$778.50