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	$69.30	12.624%	$78.0484	$78.05	$78.05	$78.00
Purchase #2	$186.94	9.558%	$204.8077	$204.81	$204.80	$204.80
Purchase #3	$122.31	7.361%	$131.3132	$131.31	$131.30	$131.30
Purchase #4	$64.74	4.254%	$67.494	$67.49	$67.50	$67.50
Purchase #5	$10.62	11.832%	$11.8766	$11.88	$11.90	$11.90
Purchase #6	$142.31	9.465%	$155.7796	$155.78	$155.80	$155.80
Purchase #7	$200.62	7.186%	$215.0366	$215.04	$215.05	$215.00
7 purchase totals =	$796.84		$864.3561	$864.36	$864.40	$864.30