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	$146.34	10.293%	$161.4028	$161.40	$161.40	$161.40
Purchase #2	$235.78	7.791%	$254.1496	$254.15	$254.15	$254.10
Purchase #3	$56.45	4.238%	$58.8424	$58.84	$58.85	$58.80
Purchase #4	$71.49	10.121%	$78.7255	$78.73	$78.75	$78.70
Purchase #5	$232.53	11.205%	$258.585	$258.59	$258.60	$258.60
Purchase #6	$246.85	13.541%	$280.276	$280.28	$280.30	$280.30
Purchase #7	$15.91	9.853%	$17.4776	$17.48	$17.50	$17.50
7 purchase totals =	$1,005.35		$1,109.4589	$1,109.47	$1,109.55	$1,109.40