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	$150.63	12.739%	$169.8188	$169.82	$169.80	$169.80
Purchase #2	$74.73	3.296%	$77.1931	$77.19	$77.20	$77.20
Purchase #3	$40.28	13.181%	$45.5893	$45.59	$45.60	$45.60
Purchase #4	$63.50	4.316%	$66.2407	$66.24	$66.25	$66.20
Purchase #5	$93.80	5.132%	$98.6138	$98.61	$98.60	$98.60
Purchase #6	$149.76	5.632%	$158.1945	$158.19	$158.20	$158.20
Purchase #7	$164.80	5.734%	$174.2496	$174.25	$174.25	$174.20
7 purchase totals =	$737.50		$789.8998	$789.89	$789.90	$789.80