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	$51.50	7.567%	$55.397	$55.40	$55.40	$55.40
Purchase #2	$245.78	13.249%	$278.3434	$278.34	$278.35	$278.30
Purchase #3	$80.43	7.497%	$86.4598	$86.46	$86.45	$86.50
Purchase #4	$80.49	4.220%	$83.8867	$83.89	$83.90	$83.90
Purchase #5	$235.58	7.161%	$252.4499	$252.45	$252.45	$252.40
Purchase #6	$97.90	9.440%	$107.1418	$107.14	$107.15	$107.10
Purchase #7	$201.71	10.606%	$223.1034	$223.10	$223.10	$223.10
7 purchase totals =	$993.39		$1,086.7820	$1,086.78	$1,086.80	$1,086.70