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	$12.48	3.809%	$12.9554	$12.96	$12.95	$13.00
Purchase #2	$150.55	3.316%	$155.5422	$155.54	$155.55	$155.50
Purchase #3	$102.54	11.300%	$114.127	$114.13	$114.15	$114.10
Purchase #4	$114.82	3.331%	$118.6447	$118.64	$118.65	$118.60
Purchase #5	$164.89	11.158%	$183.2884	$183.29	$183.30	$183.30
Purchase #6	$116.30	13.783%	$132.3296	$132.33	$132.35	$132.30
Purchase #7	$46.81	8.817%	$50.9372	$50.94	$50.95	$50.90
7 purchase totals =	$708.39		$767.8245	$767.83	$767.90	$767.70