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	$33.78	4.714%	$35.3724	$35.37	$35.35	$35.40
Purchase #2	$148.55	8.264%	$160.8262	$160.83	$160.85	$160.80
Purchase #3	$239.61	13.389%	$271.6914	$271.69	$271.70	$271.70
Purchase #4	$80.38	7.595%	$86.4849	$86.48	$86.50	$86.50
Purchase #5	$19.43	3.699%	$20.1487	$20.15	$20.15	$20.10
Purchase #6	$202.83	3.193%	$209.3064	$209.31	$209.30	$209.30
Purchase #7	$218.92	4.549%	$228.8787	$228.88	$228.90	$228.90
7 purchase totals =	$943.50		$1,012.7087	$1,012.71	$1,012.75	$1,012.70