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	$5.43	10.466%	$5.9983	$6.00	$6.00	$6.00
Purchase #2	$154.95	12.354%	$174.0925	$174.09	$174.10	$174.10
Purchase #3	$121.47	5.311%	$127.9213	$127.92	$127.90	$127.90
Purchase #4	$70.52	11.394%	$78.555	$78.56	$78.55	$78.60
Purchase #5	$125.50	13.565%	$142.5241	$142.52	$142.50	$142.50
Purchase #6	$250.93	9.385%	$274.4798	$274.48	$274.50	$274.50
Purchase #7	$221.46	5.319%	$233.2395	$233.24	$233.25	$233.20
7 purchase totals =	$950.26		$1,036.8105	$1,036.81	$1,036.80	$1,036.80