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	$81.45	10.853%	$90.2898	$90.29	$90.30	$90.30
Purchase #2	$133.30	9.736%	$146.2781	$146.28	$146.30	$146.30
Purchase #3	$19.49	10.609%	$21.5577	$21.56	$21.55	$21.60
Purchase #4	$187.50	5.785%	$198.3469	$198.35	$198.35	$198.30
Purchase #5	$142.71	12.499%	$160.5473	$160.55	$160.55	$160.50
Purchase #6	$193.47	6.709%	$206.4499	$206.45	$206.45	$206.40
Purchase #7	$51.40	5.749%	$54.355	$54.36	$54.35	$54.40
7 purchase totals =	$809.32		$877.8247	$877.84	$877.85	$877.80